Php: Fix form data field names to use spec-defined baseName instead of paramName

Author: ksvirkou-hubspot

modules/openapi-generator/src/main/resources/php/api.mustache

@@ -654,7 +654,7 @@ use {{invokerPackage}}\ObjectSerializer;
 
         $formData = $formDataProcessor->prepare([
         {{/-first}}
-            '{{paramName}}' => ${{paramName}},
+            '{{baseName}}' => ${{paramName}},
         {{#-last}}
         ]);