BKL-Removal: convert pipe to use unlocked_ioctl too

No BKL needed in pipe_ioctl

Signed-off-by: Andi Kleen <ak@suse.de>
Cc: Jens Axboe <jens.axboe@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>