[XFRM]: Fix sparse warning.

security/selinux/xfrm.c:155:10: warning: Using plain integer as NULL pointer
Signed-off-by: Luiz Capitulino <lcapitulino@mandriva.com.br>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

security/selinux/xfrm.c

@@ -146,7 +146,7 @@ static int selinux_xfrm_sec_ctx_alloc(struct xfrm_sec_ctx **ctxp, struct xfrm_us
 	return rc;
 
 out:
-	*ctxp = 0;
+	*ctxp = NULL;
 	kfree(ctx);
 	return rc;
 }