f2fs: return directly if block has been removed from the victim

commit 206147112860418fa9363cf94ec2c172bdf4313a upstream.

If one block has been to written to a new place, just return
in move data process. This patch check it again with holding
page lock.

Signed-off-by: Yunlei He <heyunlei@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>