drm/i915: Drop crtc NULL check from intel_crtc_active()

intel_crtc_active() is never called with a NULL crtc. Drop
the redundant NULL check.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231207193441.20206-5-ville.syrjala@linux.intel.com


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