vol: avoid attach retry loops on SYNC_FAILED

Avoid unnecessary volume attach retry loops if a volume
salvage is unable to be scheduled due to a hard error.

Reviewed-on: http://gerrit.openafs.org/7566
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Tom Keiser <tkeiser@sinenomine.net>
Reviewed-by: Derrick Brashear <shadow@dementix.org>
(cherry picked from commit dda5cc0c5f7172aa4edf58c0f876c8bf05590889)

Change-Id: I93760c1bd337a76079bf03dcba1d9c4e32cd692e
Reviewed-on: http://gerrit.openafs.org/9483
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>