Staging: generic_serial: fix double locking bug

spin_lock_irqsave() is not nestable.  The second time that it gets
called it overwrites the "flags" variable and so IRQs can't be restored
properly.
Signed-off-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/staging/generic_serial/generic_serial.c

@@ -566,9 +566,9 @@ void gs_close(struct tty_struct * tty, struct file * filp)
 	 * line status register.
 	 */
 
-	spin_lock_irqsave(&port->driver_lock, flags);
+	spin_lock(&port->driver_lock);
 	port->rd->disable_rx_interrupts (port);
-	spin_unlock_irqrestore(&port->driver_lock, flags);
+	spin_unlock(&port->driver_lock);
 	spin_unlock_irqrestore(&port->port.lock, flags);
 
 	/* close has no way of returning "EINTR", so discard return value */