input_common/motion_input: Make use of Common::PI constant

Also amend the copyright notice to yuzu's instead of Dolphin's, which was mistakenly copy-pasted from another file.

src/input_common/motion_input.h

@@ -1,6 +1,6 @@
-// Copyright 2014 Dolphin Emulator Project
-// Licensed under GPLv2+
-// Refer to the license.txt file included.
+// Copyright 2020 yuzu Emulator Project
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included
 
 #pragma once