power: reset: at91-poweroff: fix wakeup status register index

The wakeup status is read from Shutdown Status Register and not the
SHDW_CR which is the one at address 0.
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>

drivers/power/reset/at91-poweroff.c

@@ -51,7 +51,7 @@ static void __iomem *at91_shdwc_base;
 
 static void __init at91_wakeup_status(void)
 {
-	u32 reg = readl(at91_shdwc_base);
+	u32 reg = readl(at91_shdwc_base + AT91_SHDW_SR);
 	char *reason = "unknown";
 
 	/* Simple power-on, just bail out */