ksmbd: Fix refcount leak when invalid session is found on session lookup

When a session is found but its state is not SMB2_SESSION_VALID, It
indicates that no valid session was found, but it is missing to decrement
the reference count acquired by the session lookup, which results in
a reference count leak. This patch fixes the issue by explicitly calling
ksmbd_user_session_put to release the reference to the session.

Cc: [e-mail]
Reported-by: Alexandre <[e-mail]>
Reported-by: Stanislas Polu <[e-mail]>
Signed-off-by: Namjae Jeon <[e-mail]>
Signed-off-by: Steve French <[e-mail]>

fs/smb/server/mgmt/user_session.c

···
 	sess = ksmbd_session_lookup(conn, id);
 	if (!sess && conn->binding)
 		sess = ksmbd_session_lookup_slowpath(id);
-	if (sess && sess->state != SMB2_SESSION_VALID)
+	if (sess && sess->state != SMB2_SESSION_VALID) {
+		ksmbd_user_session_put(sess);
 		sess = NULL;
+	}
 	return sess;
 }