drm/i915/dp: Fix DP MST error after unplugging TypeC cable

This patch avoids DP MST payload error message in dmesg, as it is trying
to update the payload to the disconnected DP MST device. After DP MST
device is disconnected we should not be updating the payload and
hence remove the error.

v2: Removed the connector status check and converted from error to debug.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=111632


Signed-off-by: Srinivasan S <srinivasan.s@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1569371742-109402-1-git-send-email-srinivasan.s@intel.com