sdl_impl: Simplify make_tuple call

The purpose of make_tuple is that you don't need to explicitly type out
the types of the things that comprise said tuple.

Given this just returns default values, we can simplify this a bit.

src/input_common/sdl/sdl_impl.cpp

@@ -358,7 +358,7 @@ public:
             return std::make_tuple(x / r * (r - deadzone) / (1 - deadzone),
                                    y / r * (r - deadzone) / (1 - deadzone));
         }
-        return std::make_tuple<float, float>(0.0f, 0.0f);
+        return {};
     }
 
     bool GetAnalogDirectionStatus(Input::AnalogDirection direction) const override {