Staging: comedi: s626: Simplify a trivial if-return sequence

This patch simplify a trivial if-return sequence. Possibly combine with
a preceding function call.

Signed-off-by: Abdul Hussain <habdul@visteon.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>