Kernel: Decorate KResult with [[nodiscard]]

Author: https://github.com/bgianfo
Commit: f3cbb79f80
Pull-request: https://github.com/SerenityOS/serenity/pull/3001
Reviewed-by: https://github.com/awesomekling

Kernel/KResult.h

@@ -35,7 +35,7 @@ enum KSuccessTag {
     KSuccess
 };
 
-class KResult {
+class [[nodiscard]] KResult {
 public:
     ALWAYS_INLINE explicit KResult(int negative_e)
         : m_error(negative_e)