image: Set load_end on partial loads

image: Set load_end on partial loads

When decompressing, it's possible that the algorithm only performs
a partial decompression.
This usually happens when CONFIG_SYS_BOOTM_LEN is too small for
the uncompressed image.

When that happens, image_decomp() returns an error and *load_end == load.
The error is then handled by handle_decomp_error().

handle_decomp_error() expects the number of uncompressed bytes in
uncomp_size but receives *load_end - load == load - load == 0.

Because of this, handle_decomp_error does not report the expected
"Image too large: increase CONFIG_SYS_BOOTM_LEN" error message.

Modify the image_decomp() logic to always report the decompressed size,
even when a partial decompression happened.

Signed-off-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>