LU-7947 obdclass: Move assignment below LASSERT()

LU-7947 obdclass: Move assignment below LASSERT()

This patch moves 'loghandle->lgh_hdr' assignment call
below LASSERT(). This avoids a case when loghandle parameter
is NULL and dereferencing the NULL pointer would fault
before it reaches LASSERT().

Test-Parameters: trivial
Signed-off-by: Arshad Hussain <arshad.hussain@seagate.com>
Change-Id: Ie9bcd172a264e104dca300a8bac04d2bd132efb0
Reviewed-on: https://review.whamcloud.com/24561
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Dmitry Eremin <dmitry.eremin@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>