USB: Fix oops in PhidgetServo

The PhidgetServo causes an Oops when any of its sysfs attributes are read
or written too, making the driver useless.

Signed-off-by: Sean Young <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/usb/misc/phidgetservo.c

···
 		dev->dev = NULL;
 		goto out;
 	}
+	dev_set_drvdata(dev->dev, dev);
 
 	servo_count = dev->type & SERVO_COUNT_QUAD ? 4 : 1;