staging: comedi: addi_apci_3120: move apci3120_set_chanlist() to driver source

Move this function from the included hwdrv_apci31210.c source file to the
main driver source file.

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>