USB: fix __must_check warnings in drivers/usb/host/

Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/drivers/usb/host/ohci-dbg.c b/drivers/usb/host/ohci-dbg.c
index 534d07d..8293c1d 100644
--- a/drivers/usb/host/ohci-dbg.c
+++ b/drivers/usb/host/ohci-dbg.c
@@ -685,10 +685,11 @@
 static inline void create_debug_files (struct ohci_hcd *ohci)
 {
 	struct class_device *cldev = ohci_to_hcd(ohci)->self.class_dev;
+	int retval;
 
-	class_device_create_file(cldev, &class_device_attr_async);
-	class_device_create_file(cldev, &class_device_attr_periodic);
-	class_device_create_file(cldev, &class_device_attr_registers);
+	retval = class_device_create_file(cldev, &class_device_attr_async);
+	retval = class_device_create_file(cldev, &class_device_attr_periodic);
+	retval = class_device_create_file(cldev, &class_device_attr_registers);
 	ohci_dbg (ohci, "created debug files\n");
 }