drm/dp: Always print aux channel name in logs

Since we're about to convert everything in drm_dp_helper.c over to using
drm_dbg_*(), let's also make our logging more consistent in drm_dp_helper.c
while we're at it to ensure that we always print the name of the AUX
channel in question.

Signed-off-by: Lyude Paul <lyude@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210423184309.207645-8-lyude@redhat.com
Reviewed-by: Dave Airlie <airlied@redhat.com>