drm/amdgpu: fix GCR_GENERAL_CNTL offset for dimgrey_cavefish

dimgrey_cavefish has similar gc_10_3 ip with sienna_cichlid,
so follow its registers offset setting.

Signed-off-by: Jiansong Chen <Jiansong.Chen@amd.com>
Reviewed-by: Tao Zhou <tao.zhou1@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org