f2fs: update blkaddr in __set_data_blkaddr() for cleanup

This patch allows caller to pass blkaddr to f2fs_set_data_blkaddr()
and let __set_data_blkaddr() inside f2fs_set_data_blkaddr() to update
dn->data_blkaddr w/ last value of blkaddr.

Just cleanup, no logic changes.

Signed-off-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>