boot: android: handle boot images with missing DTB

boot: android: handle boot images with missing DTB

607b07554e2 removed the check on the return status of the
android_image_get_dtb_img_addr call from android_image_get_dtb_by_index,
which results in null pointer accesses shortly after when trying to
check the header of a nonexistent DTB.

Fixes: 607b07554e2 ("android: boot: move to andr_image_data structure")
Signed-off-by: Sam Day <me@samcday.com>
Reviewed-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>
Link: https://lore.kernel.org/r/20250123-android-handle-no-dtb-v1-1-1cb7373247da@samcday.com
Signed-off-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>