drm/vgem: Replace drm_dev_unref with drm_dev_put

This patch unifies the naming of DRM functions for reference counting
of struct drm_device. The resulting code is more aligned with the rest
of the Linux kernel interfaces.
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20180716074624.7931-1-tzimmermann@suse.de

drivers/gpu/drm/vgem/vgem_drv.c

@@ -504,7 +504,7 @@ static int __init vgem_init(void)
 static void __exit vgem_exit(void)
 {
 	drm_dev_unregister(&vgem_device->drm);
-	drm_dev_unref(&vgem_device->drm);
+	drm_dev_put(&vgem_device->drm);
 }
 
 module_init(vgem_init);