drm/vc4: Use .dumb_map_offset and .dumb_destroy defaults

This driver can use the drm_driver.dumb_destroy and
drm_driver.dumb_map_offset defaults, so no need to set them.

Cc: Eric Anholt <eric@anholt.net>
Signed-off-by: Noralf Trønnes <noralf@tronnes.org>
Reviewed-by: Eric Anholt <eric@anholt.net>
Link: https://patchwork.freedesktop.org/patch/msgid/1500837417-40580-20-git-send-email-noralf@tronnes.org

drivers/gpu/drm/vc4/vc4_drv.c

@@ -179,8 +179,6 @@ static struct drm_driver vc4_drm_driver = {
 	.gem_prime_mmap = vc4_prime_mmap,
 
 	.dumb_create = vc4_dumb_create,
-	.dumb_map_offset = drm_gem_cma_dumb_map_offset,
-	.dumb_destroy = drm_gem_dumb_destroy,
 
 	.ioctls = vc4_drm_ioctls,
 	.num_ioctls = ARRAY_SIZE(vc4_drm_ioctls),