fixes:
https://bugs.freedesktop.org/show_bug.cgi?id=28459

agd5f: apply to r1xx/r2xx as well.
Signed-off-by: Roland Scheidegger <sroland@vmware.com>
Cc: stable@kernel.org
Signed-off-by: Alex Deucher <alexdeucher@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>