Staging: comedi: range: tidy up comedi_check_chanlist()

Refactor this function to remove an extra indent level

Signed-off-by: Fred Akers <knivey@botops.net>
Reviewed-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>