tty: drop the BKL for driver/ldisc ioctl methods

Now we have pushed the lock down we can stop wrapping the call with a lock in
the tty layer.

Signed-off-by: Alan Cox <alan@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>