drm/radeon/kms: fix the regression of DVI connector check

The check of the encoder type in the commit [e00e8b5e: drm/radeon/kms:
fix analog load detection on DVI-I connectors] is obviously wrong, and
it's the culprit of the regression on my workstation with DVI-analog
connection resulting in the blank output.

Fixed the typo now.

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