libc/blkoutstream: Zero the cache to avoid random data

and skip zero cache in lib_mtdoutstream_open since it's aleady done ih mtdoutstream_puts

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

libs/libc/stream/lib_blkoutstream.c

@@ -104,6 +104,11 @@ static int blkoutstream_puts(FAR struct lib_outstream_s *self,
         }
       else if (remain < sectorsize)
         {
+          /* Set content to all 0 before caching,
+           * so no random content will be flushed
+           */
+
+          memset(stream->cache, 0, sectorsize);
           memcpy(stream->cache, ptr, remain);
           self->nput += remain;
           remain      = 0;

libs/libc/stream/lib_mtdoutstream.c

@@ -295,7 +295,7 @@ int lib_mtdoutstream_open(FAR struct lib_mtdoutstream_s *stream,
   if (node->u.i_mtd->write == NULL)
 #endif
     {
-      stream->cache = lib_zalloc(stream->geo.erasesize);
+      stream->cache = lib_malloc(stream->geo.erasesize);
       if (stream->cache == NULL)
         {
           close_mtddriver(node);