viced: Do not offline volume on successful IH_DEC

viced: Do not offline volume on successful IH_DEC

If we fail to CoW a file due to ENOSPC, we try to IH_DEC the new file
copy, and if IH_DEC fails, we take the volume offline for salvaging.
But IH_DEC returns 0 on success, not on error. So take the salvaging
path when we get non-zero.

Reviewed-on: http://gerrit.openafs.org/7054
Reviewed-by: Jeffrey Altman <jaltman@secure-endpoints.com>
Tested-by: Jeffrey Altman <jaltman@secure-endpoints.com>
(cherry picked from commit 613f14727fbb404fb7fc1cac953dda46b671222e)

Change-Id: I207ffc4db59bdbd8b80fa4ffad9210d13d76b68f
Reviewed-on: http://gerrit.openafs.org/7394
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementix.org>