boot: android: fix booting without a ramdisk

android_image_get_ramdisk() will return an error if there is no ramdisk.
Using the android image without a ramdisk worked until commit
1ce8e10f3b4b ("image: Fix up ANDROID_BOOT_IMAGE ramdisk code") because
the return code wasn't checked until then. Return -ENOENT in case
there is no ramdisk and translate that into -ENOPKG in the calling
code, which will then indicate "no ramdisk" to its caller
(boot_get_ramdisk()).

This way, we can get rid of the "*rd_data = *rd_len = 0;" in the error
path, too.

With this, I'm able to boot a linux kernel using fastboot again:

  fastboot --base 0x41000000 --header-version 2 --dtb /path/to/dtb \
  --cmdline "root=/dev/mmcblk0p1 rootwait" boot path/to/Image

Signed-off-by: Michael Walle <mwalle@kernel.org>
Reviewed-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Link: https://lore.kernel.org/r/20240729213657.2550935-1-mwalle@kernel.org
Signed-off-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>
diff --git a/include/image.h b/include/image.h
index dd4042d..2ab1707 100644
--- a/include/image.h
+++ b/include/image.h
@@ -1858,7 +1858,7 @@
  * @vendor_boot_img : Pointer to vendor boot image header
  * @rd_data:	Pointer to a ulong variable, will hold ramdisk address
  * @rd_len:	Pointer to a ulong variable, will hold ramdisk length
- * Return: 0 if succeeded, -1 if ramdisk size is 0
+ * Return: 0 if OK, -ENOPKG if no ramdisk, -EINVAL if invalid image
  */
 int android_image_get_ramdisk(const void *hdr, const void *vendor_boot_img,
 			      ulong *rd_data, ulong *rd_len);