PM: Avoid compiler warning in pm_noirq_op()

The compiler complains that calltime may be uninitialized in
pm_noirq_op(), so add extra initialization for that variable to
avoid the warning.
Signed-off-by: NRafael J. Wysocki <rjw@sisk.pl>

drivers/base/power/main.c

@@ -304,7 +304,7 @@ static int pm_noirq_op(struct device *dev,
 			pm_message_t state)
 {
 	int error = 0;
-	ktime_t calltime, delta, rettime;
+	ktime_t calltime = ktime_set(0, 0), delta, rettime;
 
 	if (initcall_debug) {
 		pr_info("calling  %s+ @ %i, parent: %s\n",