drm/i915/dp_mst: Fix forced link retrain handling in MST HPD IRQ handler

drm/i915/dp_mst: Fix forced link retrain handling in MST HPD IRQ handler

Handling of a forced link retraining debugfs request via the DP MST HPD
IRQ handler is incorrectly skipped, if the IRQ handler doesn't see any
HPD IRQs raised by the sink. Fix this by ensuring that the request is
always handled (in the Fixes: commit below by directly calling
intel_dp_check_link_state(), later by the same call moved to
intel_dp_handle_link_service_irq()).

Cc: Luca Coelho <luciano.coelho@intel.com>
Fixes: db4855d90363 ("drm/i915/dp_mst: Reuse intel_dp_check_link_state() in the HPD IRQ handler")
Reviewed-by: Suraj Kandpal <suraj.kandpal@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patch.msgid.link/20260311153152.133744-1-imre.deak@intel.com