fix: simplify initialization of PacketAcknowledgementCall in getPacketAcknowledgementCall function

Author: YukiTsuchida

src/core/CrossSimpleModule.sol

@@ -21,8 +21,9 @@ contract CrossSimpleModule is CrossModule, SimpleContractRegistry, TxAtomicSimpl
         pure
         returns (bytes memory acknowledgement)
     {
-        PacketAcknowledgementCall.Data memory ack;
-        ack.status = status;
+        PacketAcknowledgementCall.Data memory ack = PacketAcknowledgementCall.Data({
+            status: status
+        });
         return packPacketAcknowledgementCall(ack);
     }
 }