drm/i915/dp_mst: Fix getting display pointer in intel_dp_mst_compute_min_hblank()

drm/i915/dp_mst: Fix getting display pointer in intel_dp_mst_compute_min_hblank()

The MST intel_connector::encoder pointer is NULL if the connector hasn't
been enabled before, so it can't be used to retrieve the display
pointer. Use instead the crtc_state and drop the unused connector
parameter.

v2: Use the crtc_state and drop the unused connector parameter.

Fixes: a5ebe00c2ace ("drm/i915/dp: Guarantee a minimum HBlank time")
Reported-and-tested-by: Khaled Almahallawy <khaled.almahallawy@intel.com>
Closes: https://lore.kernel.org/all/16754ee4cd21d99c1e81c5953134b496dd07630f.camel@intel.com
Reviewed-by: Khaled Almahallawy <khaled.almahallawy@intel.com> #v1
Cc: Arun R Murthy <arun.r.murthy@intel.com>
Cc: Suraj Kandpal <suraj.kandpal@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250206001726.3021787-1-imre.deak@intel.com