firewire: ohci: flush MMIO writes in the interrupt handler

Make sure that interrupt event clear bit writes are executed before the
interrupt handler returns.

Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>

drivers/firewire/ohci.c

@@ -1856,7 +1856,8 @@ static irqreturn_t irq_handler(int irq, void *data)
 		spin_lock(&ohci->lock);
 		update_bus_time(ohci);
 		spin_unlock(&ohci->lock);
-	}
+	} else
+		flush_writes(ohci);
 
 	return IRQ_HANDLED;
 }