VSOCK: fix outdated sk_state value in hvs_release()

Since commit 3b4477d2 ("VSOCK: use TCP
state constants for sk_state") VSOCK has used TCP_* constants for
sk_state.

Commit b4562ca7

 ("hv_sock: add locking
in the open/close/release code paths") reintroduced the SS_DISCONNECTING
constant.

This patch replaces the old SS_DISCONNECTING with the new TCP_CLOSING
constant.

CC: Dexuan Cui <decui@microsoft.com>
CC: Cathy Avery <cavery@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Jorgen Hansen <jhansen@vmware.com>
Signed-off-by: David S. Miller <davem@davemloft.net>