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/compositor.h b/src/compositor.h
index 3722d32..fac07c7 100644
--- a/src/compositor.h
+++ b/src/compositor.h
@@ -416,7 +416,7 @@
 	      uint32_t time, int x, int y);
 void
 notify_button(struct wl_input_device *device,
-	      uint32_t time, int32_t button, int32_t state);
+	      uint32_t time, int32_t button, uint32_t state);
 void
 notify_axis(struct wl_input_device *device,
 	      uint32_t time, uint32_t axis, int32_t value);