drm/amdgpu: 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/1500837417-40580-30-git-send-email-noralf@tronnes.org

drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c

@@ -822,7 +822,6 @@ static struct drm_driver kms_driver = {
 	.gem_close_object = amdgpu_gem_object_close,
 	.dumb_create = amdgpu_mode_dumb_create,
 	.dumb_map_offset = amdgpu_mode_dumb_mmap,
-	.dumb_destroy = drm_gem_dumb_destroy,
 	.fops = &amdgpu_driver_kms_fops,
 
 	.prime_handle_to_fd = drm_gem_prime_handle_to_fd,