bootutil: Fix for flash_area_id_to_image

The function was incorrectly identifying partition of secondary slot
of image 0 as belonging to image 1, at the same time failing to
identify partition of primary slot of image 1.

Signed-off-by: Dominik Ermel <dominik.ermel@nordicsemi.no>

boot/bootutil/src/bootutil_public.c

@@ -463,7 +463,7 @@ static int flash_area_id_to_image(int id)
 #if BOOT_IMAGE_NUMBER > 2
 #error "BOOT_IMAGE_NUMBER > 2 requires change to flash_area_id_to_image"
 #elif BOOT_IMAGE_NUMBER > 1
- if (FLASH_AREA_IMAGE_SECONDARY(0) == id || (FLASH_AREA_IMAGE_SECONDARY(1) == id)) {
+ if (FLASH_AREA_IMAGE_PRIMARY(1) == id || (FLASH_AREA_IMAGE_SECONDARY(1) == id)) {
  return 1;
  }
 #else