Windows: fixup cellular make mount

Ensure that all input strings contain a trailing dot.

'fsvolume' contains the trailing dot so do not add an extra one.

Change-Id: I183581d3b06a586da872edc4af54c5e34798cdf4
Reviewed-on: http://gerrit.openafs.org/9974
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>