ksmbd: delete asynchronous work from list

When smb2_lock request is canceled by smb2_cancel or smb2_close(),
ksmbd is missing deleting async_request_entry async_requests list.
Because calling init_smb2_rsp_hdr() in smb2_lock() mark ->synchronous
as true and then it will not be deleted in
ksmbd_conn_try_dequeue_request(). This patch add release_async_work() to
release the ones allocated for async work.

Cc: stable@vger.kernel.org
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>