drm/i915: Remove bogus MST check in intel_dp_has_audio()

No idea what this MST checks is doing in intel_dp_has_audio().
Looks completely pointless, so get rid of it.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240517145356.26103-8-ville.syrjala@linux.intel.com


Reviewed-by: Jani Nikula <jani.nikula@intel.com>