blk/mtdoutstream: flush before close

Signed-off-by: buxiasen <buxiasen@xiaomi.com>

libs/libc/stream/lib_blkoutstream.c

@@ -174,6 +174,7 @@ void lib_blkoutstream_close(FAR struct lib_blkoutstream_s *stream)
 
       if (stream->cache != NULL)
         {
+          blkoutstream_flush(&stream->common);
           lib_free(stream->cache);
           stream->cache = NULL;
         }

libs/libc/stream/lib_mtdoutstream.c

@@ -240,6 +240,7 @@ void lib_mtdoutstream_close(FAR struct lib_mtdoutstream_s *stream)
 
       if (stream->cache != NULL)
         {
+          mtdoutstream_flush(&stream->common);
           lib_free(stream->cache);
           stream->cache = NULL;
         }