staging: comedi: cb_pcidas: tidy up trimpot_8402_write()

Rename this function so it has namespace associated with the driver.
Change the return type to void, it always returns '0' and the return
value is never checked.

For aesthetics, remove the 'static const' local variables. They don't
add any significant value.

Remove the 'bitstream' local variable. The 'value' passed to this
function will always be in the correct range due to s->maxdata so
the masking is not necessary. Change the type of the 'value' param
to match the callers type and write_calibration_bitstream()'s type.

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>