staging: comedi: introduce comedi_to_usb_dev()

Introduce a helper function to get a usb_device pointer from a
comedi_device pointer.

Signed-off-by: H Hartley Sweeten <[e-mail]>
Cc Ian Abbott <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/staging/comedi/comedi_usb.c

···
 EXPORT_SYMBOL_GPL(comedi_to_usb_interface);
 
 /**
+ * comedi_to_usb_dev() - comedi_device pointer to usb_device pointer.
+ * @dev: comedi_device struct
+ */
+struct usb_device *comedi_to_usb_dev(struct comedi_device *dev)
+{
+	struct usb_interface *intf = comedi_to_usb_interface(dev);
+
+	return intf ? interface_to_usbdev(intf) : NULL;
+}
+EXPORT_SYMBOL_GPL(comedi_to_usb_dev);
+
+/**
  * comedi_usb_auto_config() - Configure/probe a comedi USB driver.
  * @intf: usb_interface struct
  * @driver: comedi_driver struct

drivers/staging/comedi/comedidev.h

···
 struct usb_interface;
 
 struct usb_interface *comedi_to_usb_interface(struct comedi_device *);
+struct usb_device *comedi_to_usb_dev(struct comedi_device *);
 
 int comedi_usb_auto_config(struct usb_interface *, struct comedi_driver *,
 			   unsigned long context);