Change key/button grab bindings to take unsigned state

'state' here meaning 'is it up or down?', obviously.

Signed-off-by: Daniel Stone <daniel@fooishbar.org>
diff --git a/src/util.c b/src/util.c
index 9943820..78f6980 100644
--- a/src/util.c
+++ b/src/util.c
@@ -249,7 +249,7 @@
 
 static void
 binding_key(struct wl_keyboard_grab *grab,
-	    uint32_t time, uint32_t key, int32_t state)
+	    uint32_t time, uint32_t key, uint32_t state)
 {
 	struct binding_keyboard_grab *b =
 		container_of(grab, struct binding_keyboard_grab, grab);