IOS: Change devices to always return IPCCommandResult

This commit changes devices to always return IPCCommandResult rather
than just a return code for Open() and Close() in order to be able
to better emulate reply timing.

In hindsight, I should have considered we would want to emulate
timing when I cleaned up the device interface, but alas.
This rectifies that mistake.

Source/Core/Core/IOS/DeviceStub.cpp

@@ -12,11 +12,11 @@ namespace HLE
 {
 namespace Device
 {
-ReturnCode Stub::Open(const OpenRequest& request)
+IPCCommandResult Stub::Open(const OpenRequest& request)
 {
   WARN_LOG(IOS, "%s faking Open()", m_name.c_str());
   m_is_active = true;
-  return IPC_SUCCESS;
+  return GetDefaultReply(IPC_SUCCESS);
 }
 
 IPCCommandResult Stub::IOCtl(const IOCtlRequest& request)