fs/ecryptfs: remove kernel-doc warnings

Remove kernel-doc warnings:

fs/ecryptfs/mmap.c:270: warning: Excess function parameter 'flags'
description in 'ecryptfs_write_begin'

Message-ID: <20230731112533.214216-1-wangzhu9@huawei.com>
Signed-off-by: Zhu Wang <wangzhu9@huawei.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>