LU-1842 oi: handle failure cases for osd_oi_fini

LU-1842 oi: handle failure cases for osd_oi_fini

Sometimes the osd_oi_fini() may be called without osd_oi_init()
called firstly, or with osd_oi_init() failure. Under such cases,
the osd_device::od_oi_table may be invalid, so just skip related
OI cleanup.

Signed-off-by: Fan Yong <yong.fan@whamcloud.com>
Change-Id: I67156acbe235287e8fc98606b0449998ef6f9dd0
Reviewed-on: http://review.whamcloud.com/4218
Reviewed-by: Johann Lombardi <johann.lombardi@intel.com>
Reviewed-by: Liang Zhen <liang@whamcloud.com>
Tested-by: Hudson
Reviewed-by: James Simmons <uja.ornl@gmail.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>