Modernize std::fill with ranges

In DSPCore.cpp, there were two `std::fill` uses that could be simplified using `std::fill_n`. Due to their proximity with other `std::fill` algorithms being modernized with ranges, I chose to make these examples into the rare `std::ranges::fill_n`.

Source/Core/InputCommon/ControllerInterface/DInput/DInputJoystick.cpp

@@ -183,7 +183,7 @@ Joystick::Joystick(const LPDIRECTINPUTDEVICE8 device) : m_device(device)
 
   // Set hats to center:
   // "The center position is normally reported as -1" -MSDN
-  std::fill(std::begin(m_state_in.rgdwPOV), std::end(m_state_in.rgdwPOV), -1);
+  std::ranges::fill(m_state_in.rgdwPOV, -1);
 }
 
 Joystick::~Joystick()