zephyr: use indentation consistent across mcuboot

The original Zephyr platform support files use tabs for indentation
(to match the Zephyr project).  Since this code is all together, and
will be used as the basis for other platforms, fix this indentation to
match that used by the rest of mynewt.

This change is clean with respect to "git show -b", and only changes
the indentation of the beginning of lines.
diff --git a/boot/zephyr/main.c b/boot/zephyr/main.c
index f037a2b..9791f26 100644
--- a/boot/zephyr/main.c
+++ b/boot/zephyr/main.c
@@ -32,25 +32,25 @@
 
 #if defined(CONFIG_ARM)
 struct arm_vector_table {
-	uint32_t msp;
-	uint32_t reset;
+    uint32_t msp;
+    uint32_t reset;
 };
 
 static void do_boot(struct boot_rsp *rsp)
 {
-	struct arm_vector_table *vt;
+    struct arm_vector_table *vt;
 
-	/* The beginning of the image is the ARM vector table, containing
-	 * the initial stack pointer address and the reset vector
-	 * consecutively. Manually set the stack pointer and jump into the
-	 * reset vector
-	 */
-	vt = (struct arm_vector_table *)(rsp->br_image_addr +
-					 rsp->br_hdr->ih_hdr_size);
-	irq_lock();
-	sys_clock_disable();
-	_MspSet(vt->msp);
-	((void (*)(void))vt->reset)();
+    /* The beginning of the image is the ARM vector table, containing
+     * the initial stack pointer address and the reset vector
+     * consecutively. Manually set the stack pointer and jump into the
+     * reset vector
+     */
+    vt = (struct arm_vector_table *)(rsp->br_image_addr +
+                                     rsp->br_hdr->ih_hdr_size);
+    irq_lock();
+    sys_clock_disable();
+    _MspSet(vt->msp);
+    ((void (*)(void))vt->reset)();
 }
 #else
 /* Default: Assume entry point is at the very beginning of the image. Simply
@@ -59,44 +59,44 @@
  */
 static void do_boot(struct boot_rsp *rsp)
 {
-	void *start;
+    void *start;
 
-	start = (void *)(rsp->br_image_addr + rsp->br_hdr->ih_hdr_size);
+    start = (void *)(rsp->br_image_addr + rsp->br_hdr->ih_hdr_size);
 
-	/* Lock interrupts and dive into the entry point */
-	irq_lock();
-	((void (*)(void))start)();
+    /* Lock interrupts and dive into the entry point */
+    irq_lock();
+    ((void (*)(void))start)();
 }
 #endif
 
 void main(void)
 {
-	struct boot_rsp rsp;
-	int rc;
+    struct boot_rsp rsp;
+    int rc;
 
-	BOOT_LOG_INF("Starting bootloader");
+    BOOT_LOG_INF("Starting bootloader");
 
-	os_heap_init();
+    os_heap_init();
 
-	boot_flash_device = device_get_binding(FLASH_DRIVER_NAME);
-	if (!boot_flash_device) {
-		BOOT_LOG_ERR("Flash device not found");
-		while (1)
-			;
-	}
+    boot_flash_device = device_get_binding(FLASH_DRIVER_NAME);
+    if (!boot_flash_device) {
+        BOOT_LOG_ERR("Flash device not found");
+        while (1)
+            ;
+    }
 
-	rc = boot_go(&rsp);
-	if (rc != 0) {
-		BOOT_LOG_ERR("Unable to find bootable image");
-		while (1)
-			;
-	}
+    rc = boot_go(&rsp);
+    if (rc != 0) {
+        BOOT_LOG_ERR("Unable to find bootable image");
+        while (1)
+            ;
+    }
 
-	BOOT_LOG_INF("Bootloader chainload address: 0x%x", rsp.br_image_addr);
-	BOOT_LOG_INF("Jumping to the first image slot");
-	do_boot(&rsp);
+    BOOT_LOG_INF("Bootloader chainload address: 0x%x", rsp.br_image_addr);
+    BOOT_LOG_INF("Jumping to the first image slot");
+    do_boot(&rsp);
 
-	BOOT_LOG_ERR("Never should get here");
-	while (1)
-		;
+    BOOT_LOG_ERR("Never should get here");
+    while (1)
+        ;
 }