staging: comedi: das1800: checkpatch.pl cleanup (void function return)

Fix the checkpatch.pl warning:

WARNING: void function return statements are not generally useful

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Cc: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>