drm/i915/hdcp: Use correct function to check if encoder is HDMI

Use intel_encoder_is_hdmi function which was recently introduced to
see if encoder is HDMI or not.

--v2
-Add Fixes tag [Jani]

Fixes: 6a3691ca ("drm/i915/hdcp: Disable HDCP Line Rekeying for HDCP2.2 on HDMI")
Signed-off-by: Suraj Kandpal <suraj.kandpal@intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250117041247.1084381-1-suraj.kandpal@intel.com