drm/radeon/kms/atom: set sane defaults in atombios_get_encoder_mode()

drm/radeon/kms/atom: set sane defaults in atombios_get_encoder_mode()

commit c7a71fc761551dc8be8543f14a90d08cda4e77f9 upstream.

If there was no connector mapped to the encoder, atombios_get_encoder_mode()
returned 0 which is the id for DP.  Return something sane instead based on
the encoder id.  This avoids hitting the DP paths on non-DP encoders.

Signed-off-by: Alex Deucher <alexdeucher@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Andi Kleen <ak@linux.intel.com>