ARM: at91: fix system timer irq issue due to sparse irq support

AT91_ID_SYS as virq is incorrect because of spare irq support which
introduces NR_IRQS_LEGACY offset.
Signed-off-by: Ludovic Desroches <ludovic.desroches@atmel.com>
Tested-by: Joachim Eastwood <joachim.eastwood@jotron.com>
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>

arch/arm/mach-at91/at91rm9200_time.c

@@ -197,7 +197,7 @@ void __init at91rm9200_timer_init(void)
 	at91_st_read(AT91_ST_SR);
 
 	/* Make IRQs happen for the system timer */
-	setup_irq(AT91_ID_SYS, &at91rm9200_timer_irq);
+	setup_irq(NR_IRQS_LEGACY + AT91_ID_SYS, &at91rm9200_timer_irq);
 
 	/* The 32KiHz "Slow Clock" (tick every 30517.58 nanoseconds) is used
 	 * directly for the clocksource and all clockevents, after adjusting