f2fs: avoid to check PG_error flag

After below changes:
commit 14db0b3c ("fscrypt: stop using PG_error to track error status")
commit 98dc08ba

 ("fsverity: stop using PG_error to track error status")

There is no place in f2fs we will set PG_error flag in page, let's remove
other PG_error usage in f2fs, as a step towards freeing the PG_error flag
for other uses.

Cc: Eric Biggers <ebiggers@kernel.org>
Signed-off-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>