LZ4: compression/decompression signedness mismatch (v2)
LZ4 compression and decompression functions require different
in signedness input/output parameters: unsigned char for
compression and signed char for decompression.

Change decompression API to require '(const) unsigned char *'.

v2: minor coding style fix.

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>

Signed-off-by: Paul Reioux <reioux@gmail.com>

Signed-off-by: DooMLoRD <metoo.mememe@gmail.com