drm/i915/fb: use struct intel_display for DISPLAY_VER()

Convert a leftover struct drm_i915_private use to struct intel_display.

Reviewed-by: Suraj Kandpal <suraj.kandpal@intel.com>
Link: https://lore.kernel.org/r/20250626101712.1898434-1-jani.nikula@intel.com


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