v4l: Convert v4l2-dev to unlocked_ioctl

v4l2 implements two separate file operations for drivers that
use locked and unlocked ioctl callbacks. Since we want to remove
the ioctl file operation in favor of the unlocked variant, this
separation no longer seems helpful.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Mauro Carvalho Chehab <mchehab@redhat.com>
Acked-by: Hans Verkuil <hverkuil@xs4all.nl>
Cc: John Kacur <jkacur@redhat.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>