staging: comedi: ke_counter: minor cleanup of cnt_attach()

Cleanup the attach function a bit to follow the style of
the other comedi pci drivers.

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Cc: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>