vt_ioctl: fix lock imbalance

commit a115902f upstream.

Don't return from switch/case directly in vt_ioctl. Set ret and break
instead so that we unlock BKL.

Signed-off-by: Jiri Slaby <jirislaby@gmail.com>
Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>