fastboot: fix CRC32 chunk size checking

fastboot: fix CRC32 chunk size checking

genimage create android-sparse file with CRC32 chunk at end. When
U-Boot's fastboot receives this chunk it returns error message:
`Fail Bogus chunk size for chunk type Dont Care`

According to reference implementation of Android's sparse file format:

<https://android.googlesource.com/platform/system/core/+/refs/heads/main/
libsparse/output_file.cpp#513>

the chunk_header.total_sz is CHUNK_HEADER_LEN + 4 (CRC32 size).

Signed-off-by: Wojciech Nizinski <niziak@spox.org>
Reviewed-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>
Tested-by: Mattijs Korpershoek <mkorpershoek@baylibre.com> # on vim3
Link: https://lore.kernel.org/r/20230925103714.4153612-1-niziak@spox.org
Signed-off-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>