staging: comedi: adl_pci6208: tidy up pci6208_ao_winsn()

For aesthetics, rename this function to help with greps,

Change the type of 'chan' to match the type of the insn->chanspec
that it is derived from using the CR_CHAN macro.

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>