writeback: initialize inode members that track writeback history

[ Upstream commit 3d65ae46 ]

inode struct members that track cgroup writeback information
should be reinitialized when inode gets allocated from
kmem_cache. Otherwise, their values remain and get used by the
new inode.

Signed-off-by: Tahsin Erdogan <tahsin@google.com>
Acked-by: Tejun Heo <tj@kernel.org>
Fixes: d10c8095 ("writeback: implement foreign cgroup inode bdi_writeback switching")
Signed-off-by: Jens Axboe <axboe@fb.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Lee Jones <joneslee@google.com>
Change-Id: Ia130901467c4f6cbbc418c18462dfe34862c2a16