staging: comedi: dmm32at: remove dmm32at_ns_to_timer()

This function is not necessary. It simply returns the 'ns' value that was
passed to it.

Remove it as well as the unnecessary Step 4 check of the cmd->convert_arg.

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>