UPSTREAM: f2fs: fix to update age extent correctly during truncation

nr_free may be less than len, we should update age extent cache
w/ range [fofs, len] rather than [fofs, nr_free].

Fixes: dfcfcc6d ("f2fs: add block_age-based extent cache")
Signed-off-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
(cherry picked from commit 8c0ed062ce27f6b7f0a568cb241e2b4dd2d9e6a6)
Change-Id: I0a4546f84fd75db2f13857e4922520ab5885e845
Signed-off-by: zhaoyuenan <amktiao030215@gmail.com>