staging: comedi: adv_pci1710: tidy up pci1720_insn_write_ao()

For aesthetics, rename this function and tidy it up.

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>