flash: use MAP_SHARED for files

source/drivers/sandbox_flash.c

@@ -97,7 +97,7 @@ struct flash_dev *flash_probe(void)
 	priv->size = st.st_size;
 
 	if (!(priv->data = mmap(NULL, priv->size, PROT_READ | PROT_WRITE,
-		MAP_PRIVATE, fileno(priv->fp), 0)))
+		MAP_SHARED, fileno(priv->fp), 0)))
 		goto err_close_fp;
 
 	dev->priv = priv;