f2fs: avoid m_flags overlay when allocating more data blocks

When more than one data blocks are allocated, the F2FS_MAP_UNWRITTEN/MAPPED
flags will be overlapped by F2FS_MAP_NEW at the later times.

Signed-off-by: Kinglong Mee <kinglongmee@gmail.com>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/data.c

@@ -867,7 +867,7 @@ next_block:
 			}
 			if (err)
 				goto sync_out;
-			map->m_flags = F2FS_MAP_NEW;
+			map->m_flags |= F2FS_MAP_NEW;
 			blkaddr = dn.data_blkaddr;
 		} else {
 			if (flag == F2FS_GET_BLOCK_BMAP) {