tty: serial: fsl_lpuart: fix crash in lpuart_uport_is_active

For serdev framework, tty->dev is a NULL pointer, lpuart_uport_is_active
calling device_may_wakeup() may cause kernel NULL pointer crash, so here
add the NULL pointer check before using it.

Fixes: 4f5cb8c5 ("tty: serial: fsl_lpuart: enable wakeup source for lpuart")
Cc: stable <stable@kernel.org>
Signed-off-by: Sherry Sun <sherry.sun@nxp.com>
Link: https://lore.kernel.org/r/20230323110923.24581-1-sherry.sun@nxp.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/fsl_lpuart.c

@@ -2948,7 +2948,7 @@ static bool lpuart_uport_is_active(struct lpuart_port *sport)
 	tty = tty_port_tty_get(port);
 	if (tty) {
 		tty_dev = tty->dev;
-		may_wake = device_may_wakeup(tty_dev);
+		may_wake = tty_dev && device_may_wakeup(tty_dev);
 		tty_kref_put(tty);
 	}