USB: serial: mos7840: use irqsave() in USB's complete callback

The USB completion callback does not disable interrupts while acquiring
the lock. We want to remove the local_irq_disable() invocation from
__usb_hcd_giveback_urb() and therefore it is required for the callback
handler to disable the interrupts while acquiring the lock.
The callback may be invoked either in IRQ or BH context depending on the
USB host controller.
Use the _irqsave() variant of the locking primitives.
Signed-off-by: NJohn Ogness <john.ogness@linutronix.de>
Signed-off-by: NSebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: NJohan Hovold <johan@kernel.org>

drivers/usb/serial/mos7840.c

@@ -802,18 +802,19 @@ static void mos7840_bulk_out_data_callback(struct urb *urb)
 	struct moschip_port *mos7840_port;
 	struct usb_serial_port *port;
 	int status = urb->status;
+	unsigned long flags;
 	int i;
 
 	mos7840_port = urb->context;
 	port = mos7840_port->port;
-	spin_lock(&mos7840_port->pool_lock);
+	spin_lock_irqsave(&mos7840_port->pool_lock, flags);
 	for (i = 0; i < NUM_URBS; i++) {
 		if (urb == mos7840_port->write_urb_pool[i]) {
 			mos7840_port->busy[i] = 0;
 			break;
 		}
 	}
-	spin_unlock(&mos7840_port->pool_lock);
+	spin_unlock_irqrestore(&mos7840_port->pool_lock, flags);
 
 	if (status) {
 		dev_dbg(&port->dev, "nonzero write bulk status received:%d\n", status);