In commit 57864ae5 ("f2fs: limit # of inmemory pages"), we have
limited memory footprint of all inmem pages with 20% of total memory,
otherwise, if we exceed the threshold, we will try to drop all inmem
pages to avoid excessive memory pressure resulting in performance
regression.

But in some unrelated error paths, we will also drop all inmem pages,
which should be wrong, fix it in this patch.
Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>