misc: c2port: use dev_bin_attrs instead of hand-coding it

Classes support a list of default binary attributes, so use that in the
c2port driver, instead of hand creating and destroying the file, which
is racing with userspace.  Bonus is this removes lines of code.

Cc: Rodolfo Giometti <giometti@linux.it>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>