service: Use nested namespace specifiers where applicable

There were a few places where nested namespace specifiers weren't being
used where they could be within the service code. This amends that to
make the namespacing a tiny bit more compact.

src/core/hle/service/gsp/gsp.h

@@ -11,8 +11,7 @@
 #include "core/hle/service/gsp/gsp_gpu.h"
 #include "core/hle/service/gsp/gsp_lcd.h"
 
-namespace Service {
-namespace GSP {
+namespace Service::GSP {
 /**
  * Retrieves the framebuffer info stored in the GSP shared memory for the
  * specified screen index and thread id.
@@ -29,5 +28,4 @@ FrameBufferUpdate* GetFrameBufferInfo(u32 thread_id, u32 screen_index);
 void SignalInterrupt(InterruptId interrupt_id);
 
 void InstallInterfaces(SM::ServiceManager& service_manager);
-} // namespace GSP
-} // namespace Service
+} // namespace Service::GSP