drm/hisilicon: hibmc: 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: Chen Feng <puck.chen@hisilicon.com>
Signed-off-by: Noralf Trønnes <noralf@tronnes.org>
Reviewed-by: Sean Paul <seanpaul@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/1500837417-40580-37-git-send-email-noralf@tronnes.org

drivers/gpu/drm/hisilicon/hibmc/hibmc_drm_drv.c

@@ -67,7 +67,6 @@ static struct drm_driver hibmc_driver = {
 	.gem_free_object_unlocked = hibmc_gem_free_object,
 	.dumb_create            = hibmc_dumb_create,
 	.dumb_map_offset        = hibmc_dumb_mmap_offset,
-	.dumb_destroy           = drm_gem_dumb_destroy,
 	.irq_handler		= hibmc_drm_interrupt,
 };