cmd: Fix parsing positional args

cmd: Fix parsing positional args

If the first parameter of a libcmd syntax is a flag, cmd_Parse was
skipping over positional arguments, since j will be 0 at this point
(the j variable is only used if we're processing an explicit switch).
Effectively revert this area to what it was before
a2f1ca5fd52ac2fb7e68b101bbe3da9878c10474 so such positional parameters
work again.

Also move the j variable to inside the only block in which it is used,
to try and avoid such mistakes in the future.

Change-Id: Ifa52cecf50a3f561c70de351a9ebd026e90eeeab
Reviewed-on: http://gerrit.openafs.org/4711
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>