drm/radeon/kms: bail early in dvi_detect for digital only connectors

DVI-D and HDMI-A are digital only, so there's no need to
attempt analog load detect.  Also, skip bail before the
!force check, or we fail to get a disconnect events.
The next patches in the series attempt to fix disconnect
events for connectors with analog support (DVI-I, HDMI-B,
DVI-A).

Fixes:
https://bugs.freedesktop.org/show_bug.cgi?id=41561



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