drm/i915/hdcp: migrate away from kdev_to_i915() in GSC messaging

drm/i915/hdcp: migrate away from kdev_to_i915() in GSC messaging

Use to_intel_display() instead of kdev_to_i915() in the HDCP component
API hooks. Avoid further drive-by changes at this point, and just
convert the display pointer to i915, and leave the struct intel_display
conversion for later.

The NULL error checking in the hooks make this a bit cumbersome. I'm not
actually sure they're really required, but don't go down that rabbit
hole just now.

Cc: Gustavo Sousa <gustavo.sousa@intel.com>
Reviewed-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Reviewed-by: Suraj Kandpal <suraj.kandpal@intel.com>
Reviewed-by: Arun R Murthy <arun.r.murthy@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/efd5c4c164c01b7ee50ad43f202b074b373fb810.1724942754.git.jani.nikula@intel.com
Signed-off-by: Jani Nikula <jani.nikula@intel.com>