usb: gadget: drop superfluous ':' in doc string

usb: gadget: drop superfluous ':' in doc string

There was one superfluous ':' that kernel-doc complained about.

Reported-by: Randy Dunlap <rdunlap@infradead.org>
Closes: https://lore.kernel.org/all/c718a490-028d-2682-9ad7-8256d16504bf@infradead.org/
Fixes: fb6211f1584a ("usb: gadget: add doc to struct usb_composite_dev")
Signed-off-by: Jó Ágila Bitsch <jgilab@gmail.com>
Reviewed-by: Randy Dunlap <rdunlap@infradead.org>
Link: https://lore.kernel.org/r/ZEQFzMntIrwvZl4+@jo-einhundert
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>