[media] media DocBook: fix NV16M description

The NV16M description contained some copy-and-paste text from NV12M,
suggesting that this format is a 4:2:0 format when it really is a
4:2:2 format.

Fixed the text.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>