fs: Move mmap callback before truncate in [file|mountpt]_operations

since mmap may exist in block_operations, but truncate may not,
moving mmap beforee truncate could make three struct more compatible

Signed-off-by: Xiang Xiao <xiaoxiang@xiaomi.com>

fs/mqueue/mq_open.c

@@ -60,8 +60,8 @@ static const struct file_operations g_nxmq_fileops =
   NULL,             /* write */
   NULL,             /* seek */
   NULL,             /* ioctl */
-  NULL,             /* truncate */
   NULL,             /* mmap */
+  NULL,             /* truncate */
   nxmq_file_poll    /* poll */
 };