hle: Add proper type for result code

This should clean up all HLE errorcode in the codebase.

I didn't removed Rust::Result as this should be a cleanup for another
iteration.

src/core/services/boss.cpp

@@ -14,12 +14,6 @@ namespace BOSSCommands {
 	};
 }
 
-namespace Result {
-	enum : u32 {
-		Success = 0,
-	};
-}
-
 void BOSSService::reset() {
 	optoutFlag = 0;
 }