staging: comedi: addi_apci_3xxx: tidy up i_APCI3XXX_AnalogInputConfigOperatingMode()

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

Rename the CamelCase function and all the CamelCase local variables.

Refactor the sanity checks to 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>