drivers: tty: Fix use-after-free in pty_common_install

In 2c964a2f "drivers: tty: Merge alloc_tty_struct and
initialize_tty_struct", I messed up the refactorization of
pty_common_install, causing use-after-free and NULL pointer derefs on
various error paths. This should fix it.
Reported-by: Julia Lawall <julia.lawall@lip6.fr>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/pty.c

@@ -388,7 +388,7 @@ static int pty_common_install(struct tty_driver *driver, struct tty_struct *tty,
 	deinitialize_tty_struct(o_tty);
 	free_tty_struct(o_tty);
 err_put_module:
-	module_put(o_tty->driver->owner);
+	module_put(driver->other->owner);
 err:
 	kfree(ports[0]);
 	kfree(ports[1]);