f2fs: avoid to write during the recovery

This patch enhances the recovery routine not to write any data/node/meta until
its completion.
If any writes are sent to the disk, it could contaminate the written history
that will be used for further recovery.

Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>

diff --cc fs/f2fs/checkpoint.c
Simple merge

diff --cc fs/f2fs/node.c
Simple merge