LU-4718 osp: clear oxe_ready on old oxe

LU-4718 osp: clear oxe_ready on old oxe

In osp_xattr_get() and osp_declare_xattr_set() avoid NULL pointer
deferences in the error handling cases by clearing oxe_ready on the
old xattr cache entries.

Signed-off-by: John L. Hammond <john.hammond@intel.com>
Change-Id: I54f69e2d3e6570528e5a26bc9dd6e079a773a1a8
Reviewed-on: http://review.whamcloud.com/9672
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Fan Yong <fan.yong@intel.com>
Reviewed-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Reviewed-by: Mike Pershin <mike.pershin@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>