Merge pull request #3042 from facchinm/test_PR3037

SD: allow multiple SD instances

Author: facchinm

libraries/SD/src/SD.cpp

@@ -450,7 +450,7 @@ File SDClass::open(const char *filepath, uint8_t mode) {
 
   // there is a special case for the Root directory since its a static dir
   if (parentdir.isRoot()) {
-    if ( ! file.open(SD.root, filepath, mode)) {
+    if ( ! file.open(root, filepath, mode)) {
       // failed to open the file :(
       return File();
     }