drm/i915/display/intel_display_power: Fix incorrectly documented function __intel_display_power_put_async()

Fixes the following W=1 kernel build warning(s):

 drivers/gpu/drm/i915/display/intel_display_power.c:712: warning: expecting prototype for intel_display_power_put_async(). Prototype was for __intel_display_power_put_async() instead

Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Cc: David Airlie <airlied@gmail.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Imre Deak <imre.deak@intel.com>
Cc: intel-gfx@lists.freedesktop.org
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: Lee Jones <lee@kernel.org>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230331092607.700644-18-lee@kernel.org