drm/i915/dp/mst: Fix MST logic in intel_dp_long_pulse()

drm/i915/dp/mst: Fix MST logic in intel_dp_long_pulse()

In commit 8a2df6af1c5d ("drm/i915: Cleaning up intel_dp_hpd_pulse") some
much needed clean-up was done, but unfortunately part of the change
broke DP MST.  The real issue was setting the connector state to
disconnected in the MST case, which is good, but the code then (after
a goto) checks if the connector state is not connected and shuts down
MST if this is the case, which is bad.  With this change both SST and
MST seem to be happy.

v2: Add removed check further up in the function to be sure that MST
    is shut down when we lose the link. (Ander)

Fixes: commit 8a2df6af1c5d ("drm/i915: Cleaning up intel_dp_hpd_pulse")
cc: Sivakumar Thulasimani <sivakumar.thulasimani@intel.com>
cc: Shubhangi Shrivastava <shubhangi.shrivastava@intel.com>
cc: Ander Conselvan de Oliveira <conselvan2@gmail.com>
cc: Nathan D Ciobanu <nathan.d.ciobanu@intel.com>
Signed-off-by: Jim Bride <jim.bride@linux.intel.com>
Reviewed-by: Ander Conselvan de Oliveira <conselvan2@gmail.com>
Reviewed-by: Lyude <cpaul@redhat.com>
Signed-off-by: Ander Conselvan de Oliveira <ander.conselvan.de.oliveira@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1460394684-7036-1-git-send-email-jim.bride@linux.intel.com