Fix strings and some minor adjustment to settings

src/video_core/gpu.cpp

@@ -45,7 +45,7 @@ constexpr u64 GpuClockMultiplier(Settings::GpuClock clock) {
     switch (clock) {
     case Settings::GpuClock::Boost:
         return 256;
-    case Settings::GpuClock::Fast:
+    case Settings::GpuClock::Overclock:
         return 512;
     default:
         return 1;