media: v4l2-subdev: Fix documentation of the subdev_notifier member

Fix the name of the function that registers the subdev_notifier member
of the v4l2_subdev structure.

[Sakari Ailus: Drop _sensor from the function name.]

Signed-off-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>