staging: comedi: hwdrv_apci3120: remove need for boardinfo access

The apci3120_ai_insn_config() function is broken in this driver. It does
not follow the comedi API and will fail to work correctly.

For now just remove the need for the boardinfo access to allow additional
cleanup. The 'i_NbrAiChannel' is actually the subdevice 'n_chan' use that
instead and remove the boardinfo access.

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