staging: comedi: addi_apci_3120: absorb apci3120_cyclic_ai()

This functon is called by apci3120_ai_cmd() with one additional parameter,
'mode', The 'mode' is based on the cmd->scan_begin_src.

For aesthetics, absorb the function into apci3120_ai_cmd() and use the
cmd->scan_begin_src directly to determine the 'mode'.

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>