lib/lz4: fix token in slow decompress loop

Looks like Chenxi Mao missed a line in the non-fast-decode path
when doing the backport.

ref:
https://github.com/lz4/lz4/blob/v1.9.3/lib/lz4.c#L1930

Signed-off-by: Chenyang Zhong <zhongcy95@gmail.com>
Signed-off-by: Cyber Knight <cyberknight755@gmail.com>

Author: jjpprrrr

lib/lz4/lz4_decompress.c

@@ -398,6 +398,7 @@ static FORCE_INLINE int LZ4_decompress_generic(
 #endif
 	/* Main Loop : decode sequences */
 	while (1) {
+		token = *ip++;
 		length = token >> ML_BITS;
 
 		/* ip < iend before the increment */