vol: clear ih_synced before dropping lock

vol: clear ih_synced before dropping lock

in ih_reallyclose() clear ihP->ih_synced before dropped
the IH_LOCK.  ih_reallyclose() is already committed to
performing the OS_SYNC() call.  Failing to clear the ih_synced
flag before dropping the lock permits another thread, the ih_sync_all()
thread for example, to also conclude that it must sync the
file.

Change-Id: Icb928f7d2ec2342a57ed21b440ae0580c980e9d2
Reviewed-on: http://gerrit.openafs.org/3696
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>