Revert "tty: fix port buffer locking"

This reverts commit 925bb1ce47.

It causes lots of warnings and problems so for now, let's just revert
it.

Reported-by: <valdis.kletnieks@vt.edu>
Reported-by: Russell King <linux@armlinux.org.uk>
Reported-by: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
Reported-by: Jiri Slaby <jslaby@suse.cz>
Reported-by: Andrey Konovalov <andreyknvl@google.com>
Acked-by: Vegard Nossum <vegard.nossum@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/tty_port.c

@@ -34,9 +34,7 @@ static int tty_port_default_receive_buf(struct tty_port *port,
 	if (!disc)
 		return 0;
 
-	mutex_lock(&tty->atomic_write_lock);
 	ret = tty_ldisc_receive_buf(disc, p, (char *)f, count);
-	mutex_unlock(&tty->atomic_write_lock);
 
 	tty_ldisc_deref(disc);