f2fs crypto: make sure the encryption info is initialized on opendir(2)

This patch syncs f2fs with commit 6bc445e0 ("ext4 crypto: make
sure the encryption info is initialized on opendir(2)") from ext4.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Chao Yu <chao2.yu@samsung.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>