[AF_KEY]: suppress a warning for 64k pages.

On PowerPC allmodconfig build we get this:

net/key/af_key.c:400: warning: comparison is always false due to limited range of data type
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/key/af_key.c

@@ -395,9 +395,9 @@ static inline int pfkey_sec_ctx_len(struct sadb_x_sec_ctx *sec_ctx)
 static inline int verify_sec_ctx_len(void *p)
 {
 	struct sadb_x_sec_ctx *sec_ctx = (struct sadb_x_sec_ctx *)p;
-	int len;
+	int len = sec_ctx->sadb_x_ctx_len;
 
-	if (sec_ctx->sadb_x_ctx_len > PAGE_SIZE)
+	if (len > PAGE_SIZE)
 		return -EINVAL;
 
 	len = pfkey_sec_ctx_len(sec_ctx);