Windows: cm_GetCell_gen Fixup cm_server cellp on race

If a race occurs during the instantiation of a new cm_cell_t object,
the created servers will point at the wrong cm_cell_t object after
the race is detected.  Before cm_GetCell_gen completes the cm_server_t
objects must be fixed to point to the correct cm_cell_t.

Change-Id: I8341c2cfd2a8ac7be31699d11f78b4b9ced257af
Reviewed-on: http://gerrit.openafs.org/10777
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>