[media] Use a named union in struct v4l2_ioctl_info

Hi Mauro,

struct v4l2_ioctl_info uses an anonymous union, which is initialized
in the v4l2_ioctls table.

Unfortunately gcc < 4.6 uses a non-standard syntax for that, so trying to
compile v4l2-ioctl.c with an older gcc will fail.

It is possible to work around this by testing the gcc version, but in this
case it is easier to make the union named since it is used in only a few
places.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Reported-by: Randy Dunlap <rdunlap@xenotime.net>
Acked-by: Randy Dunlap <rdunlap@xenotime.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>