Fix bug introduced with variable rename

Summary:
^

`mutableClass` should be used instead of `clazz`

Reviewed By: LukeDefeo

Differential Revision: D39652102

fbshipit-source-id: 8ba86d39796beed79ff7cf8b37f3460facc38430

android/src/main/java/com/facebook/flipper/plugins/uidebugger/descriptors/DescriptorRegister.kt

@@ -68,9 +68,9 @@ class DescriptorRegister {
       mutableClass = mutableClass.superclass
     }
 
-    return if (register[clazz] != null) {
+    return if (register[mutableClass] != null) {
       @Suppress("unchecked_cast")
-      register[clazz] as NodeDescriptor<T>
+      register[mutableClass] as NodeDescriptor<T>
     } else {
       null
     }