viced: AFSDisk, AFSFetchVolumeStatus Int31 PartSize

viced: AFSDisk, AFSFetchVolumeStatus Int31 PartSize

The AFSDisk and AFSFetchVolumeStatus structures use signed
32-bit integers for representation partition size and
available blocks.  RoundInt64ToInt31() should be used instead
of RoundInt64ToInt32() when assigning their values.

(cherry picked from commit e8f6dfac59fe042a04a9ac5eb3c37356cb3a22a3)
Reviewed-on: http://gerrit.openafs.org/7022
Reviewed-by: Derrick Brashear <shadow@dementix.org>
Tested-by: Derrick Brashear <shadow@dementix.org>

Change-Id: Ieb55d057b09648c88cf1f8596fd934139dde3910
Reviewed-on: http://gerrit.openafs.org/7024
Tested-by: Jeffrey Altman <jaltman@secure-endpoints.com>
Reviewed-by: Jeffrey Altman <jaltman@secure-endpoints.com>