staging: comedi: ni_at_ao: cleanup dev->board_name usage

This legacy driver does no additional probing so the dev->board_name
will already be properly initialized by the comedi core before calling
the (*attach) function.

Remove the unnecessary initialization of dev->board_name and use it
when requesting the resources instead of the open-coded strings.

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