LU-7028 tgt: initialize spin lock in tgt_init()

LU-7028 tgt: initialize spin lock in tgt_init()

The spin lock lut_client_bitmap_lock was not initialized in
tgt_init().

Signed-off-by: Ashish Purkar <ashish.purkar@seagate.com>
Change-Id: I3118bc1c007d0f2b9919be17f4a429ed164f7c6c
Reviewed-on: http://review.whamcloud.com/16045
Tested-by: Jenkins
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Emoly Liu <emoly.liu@intel.com>
Reviewed-by: Grégoire Pichon <gregoire.pichon@bull.net>
Tested-by: Oleg Drokin <oleg.drokin@intel.com>