staging: skein: fix sparse warnings related to shift operator

Fix warnings:
drivers/staging/skein/skein_base.h:89:30: warning: shift too big (50) for type int
...
drivers/staging/skein/skein_base.h:89:30: warning: shift too big (39)for type int
drivers/staging/skein/skein_base.h:89:19: warning: too many warnings

Signed-off-by: Domagoj Trsan <domagoj.trsan@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/skein/skein_base.h

@@ -84,7 +84,7 @@ struct skein_1024_ctx { /* 1024-bit Skein hash context structure */
 	u8 b[SKEIN_1024_BLOCK_BYTES];	/* partial block buf (8-byte aligned) */
 };
 
-static inline int rotl_64(int x, int N)
+static inline u64 rotl_64(u64 x, u8 N)
 {
 	return (x << N) | (x >> (64 - N));
 }