drm/radeon/kms: fix analog load detection on DVI-I connectors

We digital encoders have a detect function as well (for
DP to VGA bridges), so we make sure we choose the analog
one here.

Fixes:
https://bugs.freedesktop.org/show_bug.cgi?id=47007



Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org
Signed-off-by: Dave Airlie <airlied@redhat.com>