lib/iov_iter: initialize "flags" in new pipe_buffer

mainline inclusion
from mainline-v5.17-rc6
commit 9d2231c5d74e13b2a0546fee6737ee4446017903
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I4X1GI?from=project-issue


CVE: NA

--------------------------------

The functions copy_page_to_iter_pipe() and push_pipe() can both
allocate a new pipe_buffer, but the "flags" member initializer is
missing.

Fixes: 241699cd ("new iov_iter flavour: pipe-backed")
To: Alexander Viro <viro@zeniv.linux.org.uk>
To: linux-fsdevel@vger.kernel.org
To: linux-kernel@vger.kernel.org
Cc: stable@vger.kernel.org
Signed-off-by: Max Kellermann <max.kellermann@ionos.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Zhihao Cheng <chengzhihao1@huawei.com>
Reviewed-by: Zhang Yi <yi.zhang@huawei.com>
Signed-off-by: Laibin Qiu <qiulaibin@huawei.com>