drm/radeon/kms: fix suspend on rv530 asics

Apparently only rv515 asics need the workaround
added in f24d86f1


(drm/radeon/kms: fix resume regression for some r5xx laptops).

Fixes:
https://bugs.freedesktop.org/show_bug.cgi?id=34709

Signed-off-by: Alex Deucher <alexdeucher@gmail.com>
Cc: stable@kernel.org
Signed-off-by: Dave Airlie <airlied@redhat.com>