ksmbd: fix wrong error response status by using set_smb2_rsp_status()

[ Upstream commit be0f89d4 ]

set_smb2_rsp_status() after __process_request() sets the wrong error
status. This patch resets all iov vectors and sets the error status
on clean one.

Fixes: e2b76ab8

 ("ksmbd: add support for read compound")
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>