staging: comedi: me4000: return void from ai_round_cmd_args()

This function always succeeds. Change the return type to void and
remove the unnecessary error check in me4000_ai_do_cmd().

Move the function call in me4000_ai_do_cmd_test() from before Step 1
to Step 3 where the arguments are validated. There is no reason to
get the values if the previous steps fail.

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

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>