fs: ubifs: Fix UBIFS decompression on 64 bit

Add local size_t variable to crypto_comp_decompress as intermediate
storage for destination length to avoid memory corruption and incorrect
results on 64 bit targets.

This is what linux does for the various lz compression implementations.

Signed-off-by: Paul Davey <paul.davey@alliedtelesis.co.nz>
Cc: Heiko Schocher <hs@denx.de>
Tested-by: Heiko Schocher <hs@denx.de>