locktorture: Check the correct variable for allocation failure

There is a typo so this checks the wrong variable. "chains" plural vs
"chain" singular. We already know that "chains" is non-zero.

Fixes: 7f993623e9eb ("locktorture: Add call_rcu_chains module parameter")
Signed-off-by: Dan Carpenter <[e-mail]>
Reviewed-by: Paul E. McKenney <[e-mail]>
Signed-off-by: Frederic Weisbecker <[e-mail]>

kernel/locking/locktorture.c

···
 	if (call_rcu_chains <= 0)
 		return 0;
 	call_rcu_chain = kcalloc(call_rcu_chains, sizeof(*call_rcu_chain), GFP_KERNEL);
-	if (!call_rcu_chains)
+	if (!call_rcu_chain)
 		return -ENOMEM;
 	for (i = 0; i < call_rcu_chains; i++) {
 		call_rcu_chain[i].crc_stop = false;