adev_to_drm is used everywhere, so improve recent changes
when accessing drm_device pointer from amdgpu_device.
Signed-off-by: NGuchun Chen <guchun.chen@amd.com>
Acked-by: NChristian König <christian.koenig@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>