staging: comedi: usbduxsigma: checkpatch.pl cleanup (else not useful)

Fix the checkpatch.pl warning:

WARNING: else is not generally useful after a break or return

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>