VSOCK: remove unnecessary ternary operator on return value

Rather than assign the positive errno values to ret and then
checking if it is positive and flip the sign, just return the
errno value.

Detected by CoverityScan, CID#986649 ("Logically Dead Code")

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Jorgen Hansen <jhansen@vmware.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>