drm/radeon: Use the drm_driver.dumb_destroy default

drm_gem_dumb_destroy() is the drm_driver.dumb_destroy default,
so no need to set it.

Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: Christian König <christian.koenig@amd.com>
Signed-off-by: Noralf Trønnes <noralf@tronnes.org>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1502034068-51384-16-git-send-email-noralf@tronnes.org

drivers/gpu/drm/radeon/radeon_drv.c

@@ -583,7 +583,6 @@ static struct drm_driver kms_driver = {
 	.gem_close_object = radeon_gem_object_close,
 	.dumb_create = radeon_mode_dumb_create,
 	.dumb_map_offset = radeon_mode_dumb_mmap,
-	.dumb_destroy = drm_gem_dumb_destroy,
 	.fops = &radeon_driver_kms_fops,
 
 	.prime_handle_to_fd = drm_gem_prime_handle_to_fd,