tty: Reset itty for other pty

Commit 19ffd68f816878aed456d5e87697f43bd9e3bd2b
('pty: Remove redundant itty reset') introduced a regression
whereby the other pty's linkage is not cleared on teardown.
This triggers a false positive diagnostic in testing.

Properly reset the itty linkage.

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Cc: stable <stable@vger.kernel.org> # 3.10
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --cc drivers/tty/tty_io.c
Simple merge