drm/i915/bios: fix a comment referencing struct drm_i915_private

struct intel_vbt_data is within struct intel_display nowadays, not
struct drm_i915_private.

Reviewed-by: Gustavo Sousa <gustavo.sousa@intel.com>
Link: https://lore.kernel.org/r/b7a9a7c64f41cf61749a42ed4102e04b500fde83.1746529001.git.jani.nikula@intel.com


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