drm/i915/gmbus: pass gpio reg to intel_gpio_setup()

Avoid the additional gmbus lookup on the pin.

Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220303181931.1661767-3-jani.nikula@intel.com