reduce SCRATCH_BUFSIZE to fix upload errors

code/components/jomjol_fileserver_ota/server_file.cpp

@@ -54,7 +54,7 @@ extern "C" {
 
 
 /* Scratch buffer size */
-#define SCRATCH_BUFSIZE  8192 
+#define SCRATCH_BUFSIZE  4096 
 
 struct file_server_data {
     /* Base path of file storage */