volser: allow cloning non-rw volumes

volser: allow cloning non-rw volumes

remove EROFS error which is the only thing preventing a working clone
on a non-RW.

Change-Id: Ic3d4d07519188712e9a38267fc74ebd1eaef7d8a
Reviewed-on: http://gerrit.openafs.org/6249
Reviewed-by: Jeffrey Altman <jaltman@secure-endpoints.com>
Reviewed-by: Alistair Ferguson <alistair.ferguson@mac.com>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Tested-by: Derrick Brashear <shadow@dementix.org>
Reviewed-by: Derrick Brashear <shadow@dementix.org>