drm/i915/bios: return drm_edid_product_id from get_lvds_pnp_id()

Use a more suitable type to avoid the cast.

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Acked-by: Melissa Wen <mwen@igalia.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/4dc7bfc48e65d29829843941a70c8bf97b87abcc.1712655867.git.jani.nikula@intel.com


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