tools: bpf_jit_disasm: make get_last_jit_image return unsigned

The function returns always non-negative values.

The problem has been detected using proposed semantic patch
scripts/coccinelle/tests/assign_signed_to_unsigned.cocci [1].

[1]: http://permalink.gmane.org/gmane.linux.kernel/2046107Signed-off-by: NAndrzej Hajda <a.hajda@samsung.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

tools/net/bpf_jit_disasm.c

@@ -156,8 +156,8 @@ static void put_log_buff(char *buff)
 	free(buff);
 }
 
-static int get_last_jit_image(char *haystack, size_t hlen,
-			      uint8_t *image, size_t ilen)
+static unsigned int get_last_jit_image(char *haystack, size_t hlen,
+				       uint8_t *image, size_t ilen)
 {
 	char *ptr, *pptr, *tmp;
 	off_t off = 0;