drm/msm: 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: Rob Clark <robdclark@gmail.com>
Signed-off-by: Noralf Trønnes <noralf@tronnes.org>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/1502034068-51384-13-git-send-email-noralf@tronnes.org

drivers/gpu/drm/msm/msm_drv.c

@@ -832,7 +832,6 @@ static struct drm_driver msm_driver = {
 	.gem_vm_ops         = &vm_ops,
 	.dumb_create        = msm_gem_dumb_create,
 	.dumb_map_offset    = msm_gem_dumb_map_offset,
-	.dumb_destroy       = drm_gem_dumb_destroy,
 	.prime_handle_to_fd = drm_gem_prime_handle_to_fd,
 	.prime_fd_to_handle = drm_gem_prime_fd_to_handle,
 	.gem_prime_export   = drm_gem_prime_export,