LU-7949 osd: Move assignment below LASSERT()

LU-7949 osd: Move assignment below LASSERT()

This patch moves osd_dt_dev() call and assignment of
qsd_instance below LASSERT() under function osd_declare_qid().
This avoids a case of dereferencing osd_thandle parameter
when passed as NULL. Although osd_dt_dev() does its own
checking it is better to move it below LASSERT(). Patch
also adds LASSERT() after osd_dt_dev() call.

Signed-off-by: Arshad Hussain <arshad.hussain@seagate.com>
Change-Id: I80922d372ee768c42d5d34be8222fd5e089bbda5
Reviewed-on: http://review.whamcloud.com/22428
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>