Convert notify_axis to wl_fixed_t

In preparation for the rest of the axis code changing.

Signed-off-by: Daniel Stone <daniel@fooishbar.org>
diff --git a/src/compositor.h b/src/compositor.h
index af4f94d..256ffd9 100644
--- a/src/compositor.h
+++ b/src/compositor.h
@@ -481,7 +481,7 @@
 	      enum wl_pointer_button_state state);
 void
 notify_axis(struct wl_seat *seat, uint32_t time, uint32_t axis,
-	    int32_t value);
+	    wl_fixed_t value);
 void
 notify_key(struct wl_seat *seat, uint32_t time, uint32_t key,
 	   enum wl_keyboard_key_state state);