staging: comedi: comedi_bond: no need to initialize file[]

The `char file[]` variable in `do_dev_config()` doesn't need to be
initialized as it gets overwritten with a `snprintf()`.  It just needs
to be long enough.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>