staging: comedi: das16: use comedi_bytes_per_scan()

This inline function is just a wrapper around comedi_bytes_per_scan().

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>