compositor, shell: add and use weston_surface_set_position()

Another shorthand like weston_surface_configure().

Signed-off-by: Pekka Paalanen <ppaalanen@gmail.com>
diff --git a/src/compositor.c b/src/compositor.c
index cb21eb7..ab90ded 100644
--- a/src/compositor.c
+++ b/src/compositor.c
@@ -518,6 +518,15 @@
 	surface->geometry.dirty = 1;
 }
 
+WL_EXPORT void
+weston_surface_set_position(struct weston_surface *surface,
+			    GLfloat x, GLfloat y)
+{
+	surface->geometry.x = x;
+	surface->geometry.y = y;
+	surface->geometry.dirty = 1;
+}
+
 WL_EXPORT uint32_t
 weston_compositor_get_time(void)
 {
@@ -1364,9 +1373,9 @@
 			  device->grab->x, device->grab->y);
 
 	if (wd->sprite) {
-		wd->sprite->geometry.x = device->x - wd->hotspot_x;
-		wd->sprite->geometry.y = device->y - wd->hotspot_y;
-		wd->sprite->geometry.dirty = 1;
+		weston_surface_set_position(wd->sprite,
+					    device->x - wd->hotspot_x,
+					    device->y - wd->hotspot_y);
 
 		weston_compositor_schedule_repaint(ec);
 	}