f2fs: remove unneeded f2fs_{,un}lock_op in do_recover_data()

Protecting recovery flow by using cp_rwsem is not needed, since we have
prevent triggering any checkpoint by locking cp_mutex previously.

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