lzma: fix buffer bound check error

Variable uncompressedSize references the space available, while outSizeFull is
the actual expected uncompressed size. Using the wrong value causes LzmaDecode
to return SZ_ERROR_INPUT_EOF. Problem was introduced in commit afca2942. While
at it add additional debug message.

Signed-off-by: Antonios Vamporakis <ant@area128.com>
CC: Kees Cook <keescook@chromium.org>
CC: Simon Glass <sjg@chromium.org>
CC: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>
CC: Luka Perkov <luka@openwrt.org>