MIPS: IP22: Fix hang in power button interrupt handler

The hang was caused by the use of disable_irq() from the interrupt handler
itself.  Fixed by the use of disable_irq_nosync().  The issue was
triggered by:

    commit 3aa551c9
    Author: Thomas Gleixner <tglx@linutronix.de>
    Date:   Mon Mar 23 18:28:15 2009 +0100

        genirq: add threaded interrupt handler support
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/sgi-ip22/ip22-reset.c

@@ -148,7 +148,7 @@ static irqreturn_t panel_int(int irq, void *dev_id)
 
 	if (sgint->istat1 & SGINT_ISTAT1_PWR) {
 		/* Wait until interrupt goes away */
-		disable_irq(SGI_PANEL_IRQ);
+		disable_irq_nosync(SGI_PANEL_IRQ);
 		init_timer(&debounce_timer);
 		debounce_timer.function = debounce;
 		debounce_timer.expires = jiffies + 5;