ksmbd: fix documentation for 2 functions

ksmbd_kthread_fn() and create_socket() returns 0 or error code, and not
task_struct/ERR_PTR.

Signed-off-by: Enzo Matsumiya <ematsumiya@suse.de>
Acked-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>