USB: atm: make atmdev_ops const

Make these const as they are only passed to the function
atm_dev_register and the corresponding argument is of type const.
Done using Coccinelle.

Signed-off-by: Bhumika Goyal <bhumirks@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>