net/xfrm/xfrm_state.c: fix error return code

Initialize return variable before exiting on an error path.

A simplified version of the semantic match that finds this problem is as
follows: (http://coccinelle.lip6.fr/)

// <smpl>
(
if@p1 (\(ret < 0\|ret != 0\))
 { ... return ret; }
|
ret@p1 = 0
)
... when != ret = e1
    when != &ret
*if(...)
{
  ... when != ret = e2
      when forall
 return ret;
}

// </smpl>
Signed-off-by: NJulia Lawall <Julia.Lawall@lip6.fr>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/xfrm/xfrm_state.c

@@ -1994,8 +1994,10 @@ int __xfrm_init_state(struct xfrm_state *x, bool init_replay)
 		goto error;
 
 	x->outer_mode = xfrm_get_mode(x->props.mode, family);
-	if (x->outer_mode == NULL)
+	if (x->outer_mode == NULL) {
+		err = -EPROTONOSUPPORT;
 		goto error;
+	}
 
 	if (init_replay) {
 		err = xfrm_init_replay(x);