f2fs: fix to update last_disk_size correctly

This patch fixes to update last_disk_size only when writing out page
successfully.

Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/data.c

@@ -1716,10 +1716,14 @@ write:
 		}
 	}
 
+	if (err) {
+		file_set_keep_isize(inode);
+	} else {
 		down_write(&F2FS_I(inode)->i_sem);
 		if (F2FS_I(inode)->last_disk_size < psize)
 			F2FS_I(inode)->last_disk_size = psize;
 		up_write(&F2FS_I(inode)->i_sem);
+	}
 
 done:
 	if (err && err != -ENOENT)