drm/i915/dvo: fix debug logging on unknown DID

Print DID not VID on the DID error path. Looks like a copy-paste error
from the VID error path. Clarify and clean up error logging, making them
distinguishable from each other, while at it.

Reported-by: Petru Mihancea <petrum@gmail.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=101243
Reviewed-by: Clinton Taylor <clinton.a.taylor@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170531101631.26953-1-jani.nikula@intel.com