Change button from int to uint32_t

Since you can't really have a negative button number.

Signed-off-by: Daniel Stone <daniel@fooishbar.org>
diff --git a/src/compositor-x11.c b/src/compositor-x11.c
index 304a4d5..d363572 100644
--- a/src/compositor-x11.c
+++ b/src/compositor-x11.c
@@ -485,7 +485,7 @@
 {
 	xcb_button_press_event_t *button_event =
 		(xcb_button_press_event_t *) event;
-	int button;
+	uint32_t button;
 
 	switch (button_event->detail) {
 	default: