drm/etnaviv: Optimize error handling in etnaviv_gem_new_userptr()

Refactor this function implementation so that the
drm_gem_object_unreference_unlocked() function will only be called once
in case of a failure according to the Linux coding style recommendation
for centralized exiting of functions.

Signed-off-by: Markus Elfring <[e-mail]>
[seanpaul tweaked subject]
Signed-off-by: Sean Paul <[e-mail]>
Link: http://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/gpu/drm/etnaviv/etnaviv_gem.c

···
 	get_task_struct(current);
 
 	ret = etnaviv_gem_obj_add(dev, &etnaviv_obj->base);
-	if (ret) {
-		drm_gem_object_unreference_unlocked(&etnaviv_obj->base);
-		return ret;
-	}
+	if (ret)
+		goto unreference;
 
 	ret = drm_gem_handle_create(file, &etnaviv_obj->base, handle);
-
+unreference:
 	/* drop reference from allocate - handle holds it now */
 	drm_gem_object_unreference_unlocked(&etnaviv_obj->base);
-
 	return ret;
 }