staging: comedi: addi_apci_3120: remove boardinfo 'i_AiChannelList'

All boardinfo entries have this member set as '16'. This is also the Analog
Input 'n_chan'. For aesthetics, initialize the Analog Input 'len_chanlist'
with s->n_chan and remove the boardinfo member.

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>