f2fs: write only the pages in range during defragment

@lend of filemap_write_and_wait_range is supposed to be a "offset
in bytes where the range ends (inclusive)". Subtract 1 to avoid
writing an extra page.
Signed-off-by: Fan li <fanofcode.li@samsung.com>
Reviewed-by: Chao Yu <chao2.yu@samsung.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/file.c

@@ -1686,7 +1686,7 @@ static int f2fs_defragment_range(struct f2fs_sb_info *sbi,
 
 	/* writeback all dirty pages in the range */
 	err = filemap_write_and_wait_range(inode->i_mapping, range->start,
-						range->start + range->len);
+						range->start + range->len - 1);
 	if (err)
 		goto out;