drm/radeon: fix panel scaling with eDP and LVDS bridges

commit 855f5f1d882a34e4e9dd27b299737cd3508a5624 upstream.

We were using the wrong set_properly callback so we always
ended up with Full scaling even if something else (Center or
Full aspect) was selected.

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Cc: Weng Meiling <wengmeiling.weng@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>