Docs: usb: remove :c:func: for usb_register and usb_deregister

remove :c:func: for usb_register and usb_deregister

Signed-off-by: Philipp Hortmann <philipp.g.hortmann@gmail.com>
Link: https://lore.kernel.org/r/0ace789dfbe2d4562c27d374afa5ff078efe2261.1635138058.git.philipp.g.hortmann@gmail.com


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