drm/arcpgu: Use lockless gem BO free callback

No dev->struct_mutex anywhere to be seen.

Cc: Alexey Brodkin <abrodkin@synopsys.com>
Cc: Carlos Palminha <palminha@synopsys.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1464630800-30786-25-git-send-email-daniel.vetter@ffwll.ch

drivers/gpu/drm/arc/arcpgu_drv.c

@@ -207,7 +207,7 @@ static struct drm_driver arcpgu_drm_driver = {
 	.get_vblank_counter = drm_vblank_no_hw_counter,
 	.prime_handle_to_fd = drm_gem_prime_handle_to_fd,
 	.prime_fd_to_handle = drm_gem_prime_fd_to_handle,
-	.gem_free_object = drm_gem_cma_free_object,
+	.gem_free_object_unlocked = drm_gem_cma_free_object,
 	.gem_vm_ops = &drm_gem_cma_vm_ops,
 	.gem_prime_export = drm_gem_prime_export,
 	.gem_prime_import = drm_gem_prime_import,