Convert wl_fixed_t to int in weston_output_update_zoom().

This way, we don't have to use wl_fixed_to_int() for each
call to weston_output_update_zoom(). It accepts wl_fixed_t
types and converts internally.
diff --git a/src/compositor.c b/src/compositor.c
index 788b1de..f0d405d 100644
--- a/src/compositor.c
+++ b/src/compositor.c
@@ -2356,13 +2356,17 @@
 }
 
 WL_EXPORT void
-weston_output_update_zoom(struct weston_output *output, int x, int y)
+weston_output_update_zoom(struct weston_output *output, wl_fixed_t fx, wl_fixed_t fy)
 {
 	float ratio;
+	int32_t x, y;
 
 	if (output->zoom.level <= 0)
 		return;
 
+	x = wl_fixed_to_int(fx);
+	y = wl_fixed_to_int(fy);
+
 	output->zoom.magnification = 1 / output->zoom.level;
 	ratio = 1 - (1 / output->zoom.magnification);