mmc: core: Remove redundant runtime_idle callback

The runtime PM core handles a runtime_idle callback set to NULL as one
returning 0. So, let's just set it to NULL instead.
Signed-off-by: NUlf Hansson <ulf.hansson@linaro.org>
Acked-by: NJaehoon Chung <jh80.chung@samsung.com>

drivers/mmc/core/bus.c

@@ -180,7 +180,6 @@ static int mmc_bus_resume(struct device *dev)
 #endif
 
 #ifdef CONFIG_PM_RUNTIME
-
 static int mmc_runtime_suspend(struct device *dev)
 {
 	struct mmc_card *card = mmc_dev_to_card(dev);
@@ -196,17 +195,10 @@ static int mmc_runtime_resume(struct device *dev)
 
 	return host->bus_ops->runtime_resume(host);
 }
-
-static int mmc_runtime_idle(struct device *dev)
-{
-	return 0;
-}
-
 #endif /* !CONFIG_PM_RUNTIME */
 
 static const struct dev_pm_ops mmc_bus_pm_ops = {
-	SET_RUNTIME_PM_OPS(mmc_runtime_suspend, mmc_runtime_resume,
-			mmc_runtime_idle)
+	SET_RUNTIME_PM_OPS(mmc_runtime_suspend, mmc_runtime_resume, NULL)
 	SET_SYSTEM_SLEEP_PM_OPS(mmc_bus_suspend, mmc_bus_resume)
 };