tty: Fix UML console breakage

User-Mode Linux supplies an alternate TTY_MAJOR driver for stdio console,
so the noctty check in tty_open() must apply only to VT driver tty0
devnode and not the UML console driver tty0 devnode.

Fixes: 11e1d4aa4d ("tty: Consolidate noctty checks in tty_open()")
Reported-by: Richard Weinberger <richard.weinberger@gmail.com>
Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/tty_io.c

@@ -2158,7 +2158,7 @@ retry_open:
 	read_lock(&tasklist_lock);
 	spin_lock_irq(&current->sighand->siglock);
 	noctty = (filp->f_flags & O_NOCTTY) ||
-			device == MKDEV(TTY_MAJOR, 0) ||
+			(IS_ENABLED(CONFIG_VT) && device == MKDEV(TTY_MAJOR, 0)) ||
 			device == MKDEV(TTYAUX_MAJOR, 1) ||
 			(tty->driver->type == TTY_DRIVER_TYPE_PTY &&
 			 tty->driver->subtype == PTY_TYPE_MASTER);