drm: Fix use-after-free in the shadow-attache exit code

This regression has been introduced in

commit b3f2333d
Author: Daniel Vetter <daniel.vetter@ffwll.ch>
Date:   Wed Dec 11 11:34:31 2013 +0100

    drm: restrict the device list for shadow attached drivers
Reported-by: NDave Jones <davej@redhat.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: NDavid Herrmann <dh.herrmann@gmail.com>
Signed-off-by: NDave Airlie <airlied@redhat.com>

drivers/gpu/drm/drm_pci.c

@@ -468,8 +468,8 @@ void drm_pci_exit(struct drm_driver *driver, struct pci_driver *pdriver)
 	} else {
 		list_for_each_entry_safe(dev, tmp, &driver->legacy_dev_list,
 					 legacy_dev_list) {
-			drm_put_dev(dev);
 			list_del(&dev->legacy_dev_list);
+			drm_put_dev(dev);
 		}
 	}
 	DRM_INFO("Module unloaded\n");