drm/qxl: Delete an unnecessary check before drm_gem_object_unreference_unlocked()

The drm_gem_object_unreference_unlocked() function tests whether
its argument is NULL and then returns immediately.
Thus the test around the call is not needed.

This issue was detected by using the Coccinelle software.
Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: http://patchwork.freedesktop.org/patch/msgid/913198fa-2aa4-4804-8616-dd495428c0a5@users.sourceforge.net

drivers/gpu/drm/qxl/qxl_display.c

@@ -468,8 +468,7 @@ void qxl_user_framebuffer_destroy(struct drm_framebuffer *fb)
 {
 	struct qxl_framebuffer *qxl_fb = to_qxl_framebuffer(fb);
 
-	if (qxl_fb->obj)
-		drm_gem_object_unreference_unlocked(qxl_fb->obj);
+	drm_gem_object_unreference_unlocked(qxl_fb->obj);
 	drm_framebuffer_cleanup(fb);
 	kfree(qxl_fb);
 }