xfrm: policy: fix null dereference

Julian Wiedmann says:
> +     if (!xfrm_pol_hold_rcu(ret))

Coverity spotted that ^^^ needs a s/ret/pol fix-up:

> CID 1599386:  Null pointer dereferences  (FORWARD_NULL)
> Passing null pointer "ret" to "xfrm_pol_hold_rcu", which dereferences it.

Ditch the bogus 'ret' variable.

Fixes: 563d5ca ("xfrm: switch migrate to xfrm_policy_lookup_bytype")
Reported-by: Julian Wiedmann <jwiedmann.dev@gmail.com>
Closes: https://lore.kernel.org/netdev/06dc2499-c095-4bd4-aee3-a1d0e3ec87c4@gmail.com/
Signed-off-by: Florian Westphal <fw@strlen.de>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

Author: Florian Westphal

net/xfrm/xfrm_policy.c

@@ -4429,7 +4429,7 @@ EXPORT_SYMBOL_GPL(xfrm_audit_policy_delete);
 static struct xfrm_policy *xfrm_migrate_policy_find(const struct xfrm_selector *sel,
 						    u8 dir, u8 type, struct net *net, u32 if_id)
 {
-	struct xfrm_policy *pol, *ret = NULL;
+	struct xfrm_policy *pol;
 	struct flowi fl;
 
 	memset(&fl, 0, sizeof(fl));
@@ -4465,7 +4465,7 @@ static struct xfrm_policy *xfrm_migrate_policy_find(const struct xfrm_selector *
 	if (IS_ERR_OR_NULL(pol))
 		goto out_unlock;
 
-	if (!xfrm_pol_hold_rcu(ret))
+	if (!xfrm_pol_hold_rcu(pol))
 		pol = NULL;
 out_unlock:
 	rcu_read_unlock();