drm/amdgpu/gmc7: add missing mullins case

Looks like this got missed when we ported the code from radeon.

Reviewed-by: Edward O'Callaghan <funfunctor@folklore1984.net>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org
1 file changed