tcp: Simplify error path in inet_csk_accept().

When an error occurs in inet_csk_accept(), what we should do is
only call release_sock() and set the errno to arg->err.

But the path jumps to another label, which introduces unnecessary
initialisation and tests for newsk.

Let's simplify the error path and remove the redundant NULL
checks for newsk.

Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Shakeel Butt <shakeel.butt@linux.dev>
Link: https://patch.msgid.link/20250815201712.1745332-4-kuniyu@google.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>