bootutil: Little rework of boot_find_status

In rework:
  - size has been removed from array, as it has been making array
    at least of two elements, even if scratch partition not used;
  - some variables have been localized and some removed;
  - no longer returning rc codes from flash_area_ functions on
    failure, just single point of failure-exit - it made no sense
    anyway as we can not recover from flash failure;
  - flash area pointer is now NULLified on failure, or when
    status not found.

Signed-off-by: Dominik Ermel <dominik.ermel@nordicsemi.no>
diff --git a/boot/bootutil/src/bootutil_misc.c b/boot/bootutil/src/bootutil_misc.c
index f1160e4..c715bb8 100644
--- a/boot/bootutil/src/bootutil_misc.c
+++ b/boot/bootutil/src/bootutil_misc.c
@@ -210,16 +210,13 @@
 static int
 boot_find_status(int image_index, const struct flash_area **fap)
 {
-    uint8_t magic[BOOT_MAGIC_SZ];
-    uint32_t off;
-    uint8_t areas[2] = {
+    uint8_t areas[] = {
 #if MCUBOOT_SWAP_USING_SCRATCH
         FLASH_AREA_IMAGE_SCRATCH,
 #endif
         FLASH_AREA_IMAGE_PRIMARY(image_index),
     };
     unsigned int i;
-    int rc;
 
     /*
      * In the middle a swap, tries to locate the area that is currently
@@ -230,26 +227,26 @@
      */
 
     for (i = 0; i < sizeof(areas) / sizeof(areas[0]); i++) {
-        rc = flash_area_open(areas[i], fap);
-        if (rc != 0) {
-            return rc;
+        uint8_t magic[BOOT_MAGIC_SZ];
+
+        if (flash_area_open(areas[i], fap)) {
+            break;
         }
 
-        off = boot_magic_off(*fap);
-        rc = flash_area_read(*fap, off, magic, BOOT_MAGIC_SZ);
-        flash_area_close(*fap);
-
-        if (rc != 0) {
-            return rc;
+        if (flash_area_read(*fap, boot_magic_off(*fap), magic, BOOT_MAGIC_SZ)) {
+            flash_area_close(*fap);
+            break;
         }
 
         if (BOOT_MAGIC_GOOD == boot_magic_decode(magic)) {
             return 0;
         }
 
+        flash_area_close(*fap);
     }
 
     /* If we got here, no magic was found */
+    fap = NULL;
     return -1;
 }