f2fs: skip punching hole in special condition

Now punching hole in directory is not supported in f2fs, so let's limit file
type in punch_hole().

In addition, in punch_hole if offset is exceed file size, we should skip
punching hole.

Signed-off-by: Chao Yu <chao2.yu@samsung.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>