usb: musb: dsps: compile suspend/resume only with PM_SLEEP

Depending on PM is not enough, because only PM_RUNTIME could be
selected. Fixes:

drivers/usb/musb/musb_dsps.c:703:12: warning: 'dsps_suspend' defined but not used [-Wunused-function]
drivers/usb/musb/musb_dsps.c:721:12: warning: 'dsps_resume' defined but not used [-Wunused-function]
Signed-off-by: NWolfram Sang <wsa@sang-engineering.com>
Signed-off-by: NFelipe Balbi <balbi@ti.com>

drivers/usb/musb/musb_dsps.c

@@ -774,7 +774,7 @@ static const struct of_device_id musb_dsps_of_match[] = {
 };
 MODULE_DEVICE_TABLE(of, musb_dsps_of_match);
 
-#ifdef CONFIG_PM
+#ifdef CONFIG_PM_SLEEP
 static int dsps_suspend(struct device *dev)
 {
 	struct dsps_glue *glue = dev_get_drvdata(dev);