dm-default-key: fix wrong encryption/decryption when f2fs moves blocks

Previous change ("dm-default-key, f2fs, ICE: support dm-default-key with f2fs/ICE")
supports bio->bi_crypt_skip, so this patch should address the original issue by
adding this condition.

Change-Id: I592621cf0727656726b548e0fd39e88ca26d9037
Signed-off-by: Jaegeuk Kim <jaegeuk@google.com>
Signed-off-by: Shivaprasad Hongal <shongal@codeaurora.org>
Signed-off-by: Barani Muthukumaran <bmuthuku@codeaurora.org>