Documentation: add ioctl number entry for v4l2-subdev.h

Update ioctl-number.txt for ioctl's that are defined in
<media/v4l2-subdev.h>.
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/ioctl/ioctl-number.txt

@@ -274,6 +274,7 @@ Code  Seq#(hex)	Include File		Comments
 'v'	00-1F	linux/ext2_fs.h		conflict!
 'v'	00-1F	linux/fs.h		conflict!
 'v'	00-0F	linux/sonypi.h		conflict!
+'v'	00-0F	media/v4l2-subdev.h	conflict!
 'v'	C0-FF	linux/meye.h		conflict!
 'w'	all				CERN SCI driver
 'y'	00-1F				packet based user level communications