xfrm: avoid rcu sparse warning

xfrm/xfrm_state.c:1973:21: error: incompatible types in comparison expression (different address spaces)

Harmless, but lets fix it to reduce the noise.

While at it, get rid of unneeded NULL check, its never hit:

net/ipv4/xfrm4_state.c: xfrm_state_register_afinfo(&xfrm4_state_afinfo);
net/ipv6/xfrm6_state.c: return xfrm_state_register_afinfo(&xfrm6_state_afinfo);
net/ipv6/xfrm6_state.c: xfrm_state_unregister_afinfo(&xfrm6_state_afinfo);

... are the only callsites.
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

net/xfrm/xfrm_state.c

@@ -1932,10 +1932,10 @@ EXPORT_SYMBOL(xfrm_unregister_km);
 int xfrm_state_register_afinfo(struct xfrm_state_afinfo *afinfo)
 {
 	int err = 0;
-	if (unlikely(afinfo == NULL))
-		return -EINVAL;
-	if (unlikely(afinfo->family >= NPROTO))
+
+	if (WARN_ON(afinfo->family >= NPROTO))
 		return -EAFNOSUPPORT;
+
 	spin_lock_bh(&xfrm_state_afinfo_lock);
 	if (unlikely(xfrm_state_afinfo[afinfo->family] != NULL))
 		err = -EEXIST;
@@ -1948,14 +1948,14 @@ EXPORT_SYMBOL(xfrm_state_register_afinfo);
 
 int xfrm_state_unregister_afinfo(struct xfrm_state_afinfo *afinfo)
 {
-	int err = 0;
-	if (unlikely(afinfo == NULL))
-		return -EINVAL;
-	if (unlikely(afinfo->family >= NPROTO))
+	int err = 0, family = afinfo->family;
+
+	if (WARN_ON(family >= NPROTO))
 		return -EAFNOSUPPORT;
+
 	spin_lock_bh(&xfrm_state_afinfo_lock);
 	if (likely(xfrm_state_afinfo[afinfo->family] != NULL)) {
-		if (unlikely(xfrm_state_afinfo[afinfo->family] != afinfo))
+		if (rcu_access_pointer(xfrm_state_afinfo[family]) != afinfo)
 			err = -EINVAL;
 		else
 			RCU_INIT_POINTER(xfrm_state_afinfo[afinfo->family], NULL);