drm/i915/hdcp: Check mst_port to determine connector type

Check mst_port field in intel_connector to check connector type
rather than rely on encoder as it may not be attached to connector
at times.

--v2
-Add closes tag [Imre]

Closes: https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/10898


Signed-off-by: Suraj Kandpal <suraj.kandpal@intel.com>
Reviewed-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240521081458.1500327-3-suraj.kandpal@intel.com