Kernel: Propagate errors in StorageController reset() and shutdown()

These used to signal an error with a boolean return type. We now return
a sensible errno instead.

Kernel/Storage/StorageController.h

@@ -33,8 +33,8 @@ public:
     u32 hardware_relative_controller_id() const { return m_hardware_relative_controller_id; }
 
 protected:
-    virtual bool reset() = 0;
-    virtual bool shutdown() = 0;
+    virtual ErrorOr<void> reset() = 0;
+    virtual ErrorOr<void> shutdown() = 0;
 
     virtual void complete_current_request(AsyncDeviceRequest::RequestResult) = 0;