tcp: remove redundant SOCK_DONE checks

In both tcp_splice_read() and tcp_recvmsg(), we already test
sock_flag(sk, SOCK_DONE) right before evaluating sk->sk_state,
so "!sock_flag(sk, SOCK_DONE)" is always true.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>