LU-5589 obdclass: fix NULL pointer dereference

LU-5589 obdclass: fix NULL pointer dereference

NULL pointer dereferenced without check in lsi_prepare()

Signed-off-by: Dmitry Eremin <dmitry.eremin@intel.com>
Change-Id: I144c9bcd3739c68563c7460799efa4897489a1a7
Reviewed-on: http://review.whamcloud.com/11769
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Fan Yong <fan.yong@intel.com>
Reviewed-by: James Simmons <uja.ornl@gmail.com>
Reviewed-by: John L. Hammond <john.hammond@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>