UPSTREAM: f2fs: atomic: fix to truncate pagecache before on-disk metadata truncation

We should always truncate pagecache while truncating on-disk data.

Fixes: a46bebd5 ("f2fs: synchronize atomic write aborts")
Change-Id: I46e34ae523db44034ab37a417dd68d276c53b1a0
Signed-off-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
(cherry picked from commit ebd3309a)