[JHASH]: Use const in jhash2

Use const to avoid forcing users to cast const data.
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/jhash.h

@@ -84,7 +84,7 @@ static inline u32 jhash(const void *key, u32 length, u32 initval)
 /* A special optimized version that handles 1 or more of u32s.
  * The length parameter here is the number of u32s in the key.
  */
-static inline u32 jhash2(u32 *k, u32 length, u32 initval)
+static inline u32 jhash2(const u32 *k, u32 length, u32 initval)
 {
 	u32 a, b, c, len;