vol: attach2 must always return with VOL_LOCK held

vol: attach2 must always return with VOL_LOCK held

attach2() is required to return with the VOL_LOCK held
even though it is called without it.  This must be true
for error conditions as well.  Not all error paths are
obtaining the VOL_LOCK before returning.  Add out paths for
lock held and lock unheld error cases.

Change-Id: Ib6a05a9bafd9eb3a26a1dd3881d19baa6d59a05e
Reviewed-on: http://gerrit.openafs.org/3177
Tested-by: Derrick Brashear <shadow@dementia.org>
Reviewed-by: Jeffrey Altman <jaltman@openafs.org>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>