f2fs: check zone write pointer points to the end of zone

We don't need to report an issue, when the zone write pointer already
points to the end of the zone, since the zone mismatch is already taken
care.

Signed-off-by: Daeho Jeong <daehojeong@google.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>