bugfix: disable usb for all usb funcs

USB should be disabled if any usb func is enabled.

fix #477

Signed-off-by: Jun Li <jun.r.li@intel.com>
diff --git a/boot/zephyr/main.c b/boot/zephyr/main.c
index e276454..d114522 100644
--- a/boot/zephyr/main.c
+++ b/boot/zephyr/main.c
@@ -75,7 +75,7 @@
                                      rsp->br_hdr->ih_hdr_size);
     irq_lock();
     sys_clock_disable();
-#ifdef CONFIG_BOOT_SERIAL_CDC_ACM
+#ifdef CONFIG_USB
     /* Disable the USB to prevent it from firing interrupts */
     usb_disable();
 #endif