Windows: change thyper to offset and fix error

Windows: change thyper to offset and fix error

In cm_ReadMountPoint and cm_HandleLink the variable 'thyper'
represets the 'offset' at which cm_GetData should fetch data.
Rename 'thyper' to 'offset' and fix a coding error caused by
misinterpreting the variable purpose.

Change-Id: If60669d850f4bfba2aae6e4aaf642f7ec6f920b2
Reviewed-on: http://gerrit.openafs.org/4501
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Reviewed-by: Jeffrey Altman <jaltman@openafs.org>
Tested-by: Jeffrey Altman <jaltman@openafs.org>