ARM: 6460/1: ixp2000: fix type of ixp2000_timer_interrupt

This fixes a build warning existing since at least 2.6.30:

	arch/arm/mach-ixp2000/core.c:217: warning: initialization from incompatible pointer type
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/mach-ixp2000/core.c

@@ -197,7 +197,7 @@ unsigned long ixp2000_gettimeoffset (void)
 	return offset / ticks_per_usec;
 }
 
-static int ixp2000_timer_interrupt(int irq, void *dev_id)
+static irqreturn_t ixp2000_timer_interrupt(int irq, void *dev_id)
 {
 	/* clear timer 1 */
 	ixp2000_reg_wrb(IXP2000_T1_CLR, 1);