DynamicTablesPkg: Clear pointer in node creation fcts

The following functions:
- AmlCreateRootNode()
- AmlCreateObjectNode()
- AmlCreateDataNode()
create a node and return it by populating a pointer. This pointer
should only be considered/used if the function returns successfully.
Otherwise, the value stored in this pointer should be ignored.

For their error handling, some other functions assume that this
pointer is reset to NULL if an error occurs during a node creation.
To make this assumption correct, explicitly clear this input pointer.

Reviewed-by: Sami Mujawar <sami.mujawar@arm.com>
Signed-off-by: Pierre Gondois <Pierre.Gondois@arm.com>

DynamicTablesPkg/Library/Common/AmlLib/CodeGen/AmlCodeGen.c

@@ -22,7 +22,9 @@
   @param [in]  Node           Newly created node.
   @param [in]  ParentNode     If provided, set ParentNode as the parent
                               of the node created.
-  @param [out] NewObjectNode  If success, contains the created object node.
+  @param [out] NewObjectNode  If not NULL:
+                               - and Success, contains the created Node.
+                               - and Error, reset to NULL.
 
   @retval  EFI_SUCCESS            The function completed successfully.
   @retval  EFI_INVALID_PARAMETER  Invalid parameter.
@@ -39,7 +41,7 @@ LinkNode (
   EFI_STATUS    Status;
 
   if (NewObjectNode != NULL) {
-    *NewObjectNode = Node;
+    *NewObjectNode = NULL;
   }
 
   // Add RdNode as the last element.
@@ -51,6 +53,10 @@ LinkNode (
     }
   }
 
+  if (NewObjectNode != NULL) {
+    *NewObjectNode = Node;
+  }
+
   return EFI_SUCCESS;
 }