drm/omapdrm: 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: Tomi Valkeinen <tomi.valkeinen@ti.com>
Signed-off-by: Noralf Trønnes <noralf@tronnes.org>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1500837417-40580-31-git-send-email-noralf@tronnes.org

drivers/gpu/drm/omapdrm/omap_drv.c

@@ -517,7 +517,6 @@ static struct drm_driver omap_drm_driver = {
 	.gem_vm_ops = &omap_gem_vm_ops,
 	.dumb_create = omap_gem_dumb_create,
 	.dumb_map_offset = omap_gem_dumb_map_offset,
-	.dumb_destroy = drm_gem_dumb_destroy,
 	.ioctls = ioctls,
 	.num_ioctls = DRM_OMAP_NUM_IOCTLS,
 	.fops = &omapdriver_fops,