HID: Switch hiddev to unlocked_ioctl

Push down the BKL. In some cases compat_ioctl already doesn't take the
BKL so we don't either. Some of the locking here seems already dubious
and object lifetimes want documenting

Signed-off-by: Alan Cox <alan@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>