PM: Fix build issue in clock_ops.c for CONFIG_PM_RUNTIME unset

Fix a build issue in drivers/base/power/clock_ops.c occuring when
CONFIG_PM_RUNTIME is not set.
Signed-off-by: NRafael J. Wysocki <rjw@sisk.pl>

drivers/base/power/clock_ops.c

@@ -380,6 +380,7 @@ static int pm_runtime_clk_notify(struct notifier_block *nb,
 {
 	struct pm_clk_notifier_block *clknb;
 	struct device *dev = data;
+	char *con_id;
 
 	dev_dbg(dev, "%s() %ld\n", __func__, action);