Windows: cm_MergeStatus now returns an error code

Windows: cm_MergeStatus now returns an error code

cm_MergeStatus() can fail if the AFSFetchStatus InterfaceVersion
field does not have the value 0x1 as that is the only version that
is defined by the protocol.  The return code will be CM_ERROR_INVAL.
cm_MergeStatus() returns 0 on success.

Update all of the call sites.

Change-Id: Iddf56f68dfa26b0f11744b905a70d7d39ad853d1
Reviewed-on: http://gerrit.openafs.org/8402
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>