staging: comedi: serial2000: reduce indent level of serial2002_setup_subdevs()

Tidy up this function a bit to reduce the indent level.

This also fixex 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>