lz4: fix compression/decompression signedness mismatch

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 *".

Signed-off-by: Sergey Senozhatsky <[e-mail]>
Cc: Kyungsik Lee <[e-mail]>
Cc: Geert Uytterhoeven <[e-mail]>
Cc: Yann Collet <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

include/linux/lz4.h

···
  *	note :  Destination buffer must be already allocated.
  *		slightly faster than lz4_decompress_unknownoutputsize()
  */
-int lz4_decompress(const char *src, size_t *src_len, char *dest,
-		size_t actual_dest_len);
+int lz4_decompress(const unsigned char *src, size_t *src_len,
+		unsigned char *dest, size_t actual_dest_len);
 
 /*
  * lz4_decompress_unknownoutputsize()
···
  *		  Error if return (< 0)
  *	note :  Destination buffer must be already allocated.
  */
-int lz4_decompress_unknownoutputsize(const char *src, size_t src_len,
-		char *dest, size_t *dest_len);
+int lz4_decompress_unknownoutputsize(const unsigned char *src, size_t src_len,
+		unsigned char *dest, size_t *dest_len);
 #endif

lib/lz4/lz4_decompress.c

···
 	return (int) (-(((char *) ip) - source));
 }
 
-int lz4_decompress(const char *src, size_t *src_len, char *dest,
-		size_t actual_dest_len)
+int lz4_decompress(const unsigned char *src, size_t *src_len,
+		unsigned char *dest, size_t actual_dest_len)
 {
 	int ret = -1;
 	int input_len = 0;
···
 EXPORT_SYMBOL(lz4_decompress);
 #endif
 
-int lz4_decompress_unknownoutputsize(const char *src, size_t src_len,
-		char *dest, size_t *dest_len)
+int lz4_decompress_unknownoutputsize(const unsigned char *src, size_t src_len,
+		unsigned char *dest, size_t *dest_len)
 {
 	int ret = -1;
 	int out_len = 0;