media: v4l: async: Fix kerneldoc documentation for async functions

Fix kerneldoc documentation for functions that add async sub-devices to
notifiers. The functions themselves were improved recently but that left
issues with the kerneldoc documentation. Fix them now.

Also remove underscores from macro argument names.

[mchehab: fix a build breakage]
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Fixes: b01edcbd

 ("media: v4l2-async: Improve v4l2_async_notifier_add_*_subdev() API")
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>