Make struct CallBack indentation uniform again

Align the per-field comments.

Change-Id: Ic9da32851c518b29e110fb80428a1f261bbd9cbf
Reviewed-on: http://gerrit.openafs.org/10929
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>