Revert "f2fs: move i_size_write in f2fs_write_end"

This reverts commit a2ee0a30.

When testing with generic/032 of xfstest suit, failure message will be
reported as below:

generic/032 8s ... [failed, exit status 1] - output mismatch (see results/generic/032.out.bad)
    --- tests/generic/032.out	2015-01-11 16:52:27.643681072 +0800
    +++ results/generic/032.out.bad	2016-08-06 13:44:43.861330500 +0800
    @@ -1,5 +1,5 @@
     QA output created by 032
    -100 iterations
    -0000000 cdcd cdcd cdcd cdcd cdcd cdcd cdcd cdcd
    -*
    -0100000
    +1: [768..775]: unwritten
    +Unwritten extents found!
    ...
    (Run 'diff -u tests/generic/032.out results/generic/032.out.bad'  to see the entire diff)
Ran: generic/032
Failures: generic/032
Failed 1 of 1 tests

In write_end(), we should update i_size of inode before unlock page,
otherwise, we will lose newly updated data in following race condition.

Thread A			Thread B
- write_end
 - unlock page
				- writepages
				 - lock_page
				  - writepage
				  if page is out-of-range of file size,
				  we will skip writting the page.
 - update i_size
Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/data.c

@@ -1699,11 +1699,11 @@ static int f2fs_write_end(struct file *file,
 	trace_f2fs_write_end(inode, pos, len, copied);
 
 	set_page_dirty(page);
-	f2fs_put_page(page, 1);
 
 	if (pos + copied > i_size_read(inode))
 		f2fs_i_size_write(inode, pos + copied);
 
+	f2fs_put_page(page, 1);
 	f2fs_update_time(F2FS_I_SB(inode), REQ_TIME);
 	return copied;
 }