clocksource/drivers/h8300_timer8: Fix irq return value check

The value returned in case of error for the 'irq_of_parse_and_map' function is
zero in case of error. Fix the check in the init code.

Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
diff --git a/drivers/clocksource/h8300_timer8.c b/drivers/clocksource/h8300_timer8.c
index 2433325..3eedeff 100644
--- a/drivers/clocksource/h8300_timer8.c
+++ b/drivers/clocksource/h8300_timer8.c
@@ -230,7 +230,7 @@
 	}
 
 	irq = irq_of_parse_and_map(node, 0);
-	if (irq < 0) {
+	if (!irq) {
 		pr_err("failed to get irq for clockevent\n");
 		goto unmap_reg;
 	}