USB: Turn interface_to_usbdev into an inline function

The stronger type-checking would have prevented a bug I had.
Signed-off-by: Matthew Wilcox <willy@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

include/linux/usb.h

@@ -184,8 +184,6 @@ struct usb_interface {
 	struct work_struct reset_ws;	/* for resets in atomic context */
 };
 #define	to_usb_interface(d) container_of(d, struct usb_interface, dev)
-#define	interface_to_usbdev(intf) \
-	container_of(intf->dev.parent, struct usb_device, dev)
 
 static inline void *usb_get_intfdata(struct usb_interface *intf)
 {
@@ -493,6 +491,11 @@ struct usb_device {
 };
 #define	to_usb_device(d) container_of(d, struct usb_device, dev)
 
+static inline struct usb_device *interface_to_usbdev(struct usb_interface *intf)
+{
+	return to_usb_device(intf->dev.parent);
+}
+
 extern struct usb_device *usb_get_dev(struct usb_device *dev);
 extern void usb_put_dev(struct usb_device *dev);