staging: fix go7007-usb license

From: Randy Dunlap <[email protected]>

Add MODULE_LICENSE() for this source module to fix build warning:

WARNING: modpost: missing MODULE_LICENSE() in drivers/staging/media/go7007/go7007-usb.o see include/linux/module.h for more information

---
 drivers/staging/media/go7007/go7007-usb.c |    1 +
 1 file changed, 1 insertion(+)

@@ -1279,3 +1279,4 @@ static struct usb_driver go7007_usb_driv
 };
 
 module_usb_driver(go7007_usb_driver);
+MODULE_LICENSE("GPL v2");