drm/i915/tc: Drop extra TC cold blocking from intel_tc_port_connected()

After the previous patch the driver holds a power domain blocking
TC-cold whenever the port is locked, so we can remove the extra blocking
around the lock/unlock sequence.

Cc: José Roberto de Souza <jose.souza@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: José Roberto de Souza <jose.souza@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210921002313.1132357-13-imre.deak@intel.com