staging: comedi: adl_pci9118: tidy up check_channel_list()

staging: comedi: adl_pci9118: tidy up check_channel_list()

Rename this function to give it namespace associated with the driver.

Currently this function is called by both the AI (*do_cmdtest) and the (*do_cmd)
functions. It really only needs to be called by the (*do_cmdtest) to validate
that the chanlist meets the requirements of the hardware. It's only called by
the (*do_cmd) to verify that the scan length is not to large after adding the
extra samples needed to satisfy the DMA.

Move the extra scan length check into the (*do_cmd) function and remove the
unnecessary parameters 'frontadd' and 'backadd'.

Tidy up the reset of the function.

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>