drm/mgag200: remove the default io_mem_pfn set

The default interface situation has been taken into the framework, so
remove the default set of each module.
Signed-off-by: NTan Xiaojun <tanxiaojun@huawei.com>
Reviewed-by: NChristian König <christian.koenig@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/mgag200/mgag200_ttm.c

@@ -237,7 +237,6 @@ struct ttm_bo_driver mgag200_bo_driver = {
 	.verify_access = mgag200_bo_verify_access,
 	.io_mem_reserve = &mgag200_ttm_io_mem_reserve,
 	.io_mem_free = &mgag200_ttm_io_mem_free,
-	.io_mem_pfn = ttm_bo_default_io_mem_pfn,
 };
 
 int mgag200_mm_init(struct mga_device *mdev)