hexdump: use const notation

Trivial fix: mark the buffer to hexdump as const so callers could avoid
casting their const buffers when calling print_hex_dump().

The patch is really trivial and I suggest to consider it as a fix
(it fixes GCC warnings) and push it to current tree.
Signed-off-by: NArtem Bityutskiy <Artem.Bityutskiy@nokia.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

include/linux/kernel.h

@@ -224,7 +224,7 @@ extern void hex_dump_to_buffer(const void *buf, size_t len,
 				char *linebuf, size_t linebuflen, bool ascii);
 extern void print_hex_dump(const char *level, const char *prefix_str,
 				int prefix_type, int rowsize, int groupsize,
-				void *buf, size_t len, bool ascii);
+				const void *buf, size_t len, bool ascii);
 extern void print_hex_dump_bytes(const char *prefix_str, int prefix_type,
 			void *buf, size_t len);
 #define hex_asc(x)	"0123456789abcdef"[x]

lib/hexdump.c

@@ -145,9 +145,9 @@ EXPORT_SYMBOL(hex_dump_to_buffer);
  */
 void print_hex_dump(const char *level, const char *prefix_str, int prefix_type,
 			int rowsize, int groupsize,
-			void *buf, size_t len, bool ascii)
+			const void *buf, size_t len, bool ascii)
 {
-	u8 *ptr = buf;
+	const u8 *ptr = buf;
 	int i, linelen, remaining = len;
 	unsigned char linebuf[200];