staging: comedi: addi_apci_3120: remove scanning from ai (*insn_read)

(*insn_read) functions are supposed to do simple polled reads of a single
channel. This driver tries to be tricky and allow passing a chanlist in
the analog input (*insn_config) to allow the (*insn_read) to do chanlist
scanning with or without interrupts.

The (*insn_config) doesn't follow the comedi API and this operation mode
is not part of the API.

Remove the scanning support from the (*insn_read) as well as the support
code in the (*insn_config) and interrupt handler.

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>