Docs: usb: update comment and code near increment usage count

update comment: increment our usage count ..
and code according to usb-skeleton.c

Signed-off-by: Philipp Hortmann <philipp.g.hortmann@gmail.com>
Link: https://lore.kernel.org/r/38c6205d6b5c612902f9c187154c05e9cca51107.1635591623.git.philipp.g.hortmann@gmail.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>