InputCommon: Use nested namespace specifiers where applicable

Source/Core/DolphinQt/Config/Mapping/MappingCommon.h

@@ -11,14 +11,11 @@ class QString;
 class OutputReference;
 class QPushButton;
 
-namespace ciface
-{
-namespace Core
+namespace ciface::Core
 {
 class DeviceContainer;
 class DeviceQualifier;
-}  // namespace Core
-}  // namespace ciface
+}  // namespace ciface::Core
 
 namespace MappingCommon
 {

Source/Core/DolphinQt/Config/Mapping/MappingWidget.h

@@ -25,13 +25,10 @@ class ControlGroup;
 class EmulatedController;
 }  // namespace ControllerEmu
 
-namespace ciface
-{
-namespace Core
+namespace ciface::Core
 {
 class Device;
-}
-}  // namespace ciface
+}  // namespace ciface::Core
 
 constexpr int INDICATOR_UPDATE_FREQ = 30;