FROMGIT: f2fs: fix wrong calculation of block age

Currently we wrongly calculate the new block age to
old * LAST_AGE_WEIGHT / 100.

Fix it to new * (100 - LAST_AGE_WEIGHT) / 100
                + old * LAST_AGE_WEIGHT / 100.

Bug: 267580491
(cherry picked from commit b03a41a4
 https://git.kernel.org/pub/scm/linux/kernel/git/jaegeuk/f2fs.git

 dev)
Signed-off-by: qixiaoyu1 <qixiaoyu1@xiaomi.com>
Signed-off-by: xiongping1 <xiongping1@xiaomi.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
Change-Id: If06f04c63f9ed0de4e1d734936d9ea9a6c613d64