Apply clang-tidy fixes for llvm-else-after-return in IRCore.cpp (NFC)

Author: joker-eph

mlir/lib/Bindings/Python/IRCore.cpp

@@ -981,8 +981,7 @@ MlirDialect PyDialects::getDialectForKey(const std::string &key,
     std::string msg = (Twine("Dialect '") + key + "' not found").str();
     if (attrError)
       throw py::attribute_error(msg);
-    else
-      throw py::index_error(msg);
+    throw py::index_error(msg);
   }
   return dialect;
 }