Use correct type for reference array

Author: thk123

jbmc/src/java_bytecode/java_types.cpp

@@ -209,7 +209,7 @@ typet java_type_from_char(char t)
   case 'f': return java_float_type();
   case 'd': return java_double_type();
   case 'z': return java_boolean_type();
-  case 'a': return java_reference_type(void_typet());
+  case 'a': return java_lang_object_type();
   default:
     UNREACHABLE;
   }