f2fs: fix to read source block before invalidating it

f2fs_allocate_data_block() invalidates old block address and enable new block
address. Then, if we try to read old block by f2fs_submit_page_bio(), it will
give WARN due to reading invalid blocks.

Let's make the order sanely back.

Change-Id: I48aef01df9b7b5700fddf8fae5dbfedb59c91e78
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
Git-commit: 543b8c468f55f27f3c0178a22a91a51aabbbc428
Git-repo: https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/


Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>