mmc: core: check PM_SLEEP for mmc_bus_suspend/resume callbacks

If PM_SLEEP is not enabled, mmc.c will give warnning since mmc_bus_suspend/
mmc_bus_resume functions are defined but not used. This patch can fix this
warnning.
Reported-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Chuanxiao Dong <chuanxiao.dong@intel.com>
Signed-off-by: Chris Ball <cjb@laptop.org>

drivers/mmc/core/bus.c

@@ -122,6 +122,7 @@ static int mmc_bus_remove(struct device *dev)
 	return 0;
 }
 
+#ifdef CONFIG_PM_SLEEP
 static int mmc_bus_suspend(struct device *dev)
 {
 	struct mmc_driver *drv = to_mmc_driver(dev->driver);
@@ -143,6 +144,7 @@ static int mmc_bus_resume(struct device *dev)
 		ret = drv->resume(card);
 	return ret;
 }
+#endif
 
 #ifdef CONFIG_PM_RUNTIME