net: filter: remove unused variable and fix warning

bpf_getsockopt bpf call sets the ret variable to zero and
never changes it.  What's worse in case CONFIG_INET is
not selected the variable is completely unused generating
a warning.

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Quentin Monnet <quentin.monnet@netronome.com>
Acked-by: Lawrence Brakmo <brakmo@fb.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/filter.c

@@ -3288,7 +3288,6 @@ BPF_CALL_5(bpf_getsockopt, struct bpf_sock_ops_kern *, bpf_sock,
 	   int, level, int, optname, char *, optval, int, optlen)
 {
 	struct sock *sk = bpf_sock->sk;
-	int ret = 0;
 
 	if (!sk_fullsock(sk))
 		goto err_clear;
@@ -3308,7 +3307,7 @@ BPF_CALL_5(bpf_getsockopt, struct bpf_sock_ops_kern *, bpf_sock,
 	} else {
 		goto err_clear;
 	}
-	return ret;
+	return 0;
 #endif
 err_clear:
 	memset(optval, 0, optlen);