staging: comedi: adv_pci1710: rename pci171x_ao_insn_write()

Rename this function so it has namespace associated with the driver.

For aesthetics, move the function so it is located in the middle of
the analog input support functions.

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>