f2fs: clear PageError on writepage

Cherry-pick from origin/upstream-f2fs-stable-linux-3.18.y:
commit da4febfa ("f2fs: clear PageError on writepage")

This patch clears PageError in some pages tagged by read path, but when we
write the pages with valid contents, writepage should clear the bit likewise
ext4.

Change-Id: I3348bb48b333d1336aa6e8e03b12169569f673d5
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>