staging: comedi: addi_apci_3xxx: tidy up i_APCI3XXX_InsnConfigAnalogInput()

The analog input subdevice is broken in this driver. To help fix
it, tidy up this (*insn_config) function.

Rename the CamelCase function.

Move the (insn->n == 4) test from i_APCI3XXX_AnalogInputConfigOperatingMode()
to this function.

Make the function a bit more concise and remove the printk noise.

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>