md/raid5: add missing spin_lock_init.

commit b17459c05000fdbe8d10946570a26510f86ec0f
   raid5: add a per-stripe lock

added a spin_lock to the 'stripe_head' struct.
Unfortunately there are two places where this struct is allocated
but the spin lock was only initialised in one of them.

So add the missing spin_lock_init.

Signed-off-by: NeilBrown <neilb@suse.de>

drivers/md/raid5.c

@@ -1591,6 +1591,7 @@ static int resize_stripes(struct r5conf *conf, int newsize)
 		#ifdef CONFIG_MULTICORE_RAID456
 		init_waitqueue_head(&nsh->ops.wait_for_ops);
 		#endif
+		spin_lock_init(&nsh->stripe_lock);
 
 		list_add(&nsh->lru, &newstripes);
 	}