bpf: sockmap, fix uninitialized variable

There is a potential execution path in which variable err is
returned without being properly initialized previously.

Fix this by initializing variable err to 0.

Addresses-Coverity-ID: 1468964 ("Uninitialized scalar variable")
Fixes: e5cd3abcb31a ("bpf: sockmap, refactor sockmap routines to work with hashmap")
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

kernel/bpf/sockmap.c

@@ -1713,7 +1713,7 @@ static int __sock_map_ctx_update_elem(struct bpf_map *map,
 	struct smap_psock_map_entry *e = NULL;
 	struct smap_psock *psock;
 	bool new = false;
-	int err;
+	int err = 0;
 
 	/* 1. If sock map has BPF programs those will be inherited by the
 	 * sock being added. If the sock is already attached to BPF programs