applets/swkbd: Address comments

src/core/frontend/applets/swkbd.cpp

@@ -132,7 +132,7 @@ ValidationError SoftwareKeyboard::Finalize(const std::string& text, u8 button) {
     return ValidationError::None;
 }
 
-bool SoftwareKeyboard::DataReady() {
+bool SoftwareKeyboard::DataReady() const {
     return data_ready;
 }
 

src/core/frontend/applets/swkbd.h

@@ -93,7 +93,7 @@ public:
     /**
      * Whether the result data is ready to be received.
      */
-    bool DataReady();
+    bool DataReady() const;
 
     /**
      * Receives the current result data stored in the applet, and clears the ready state.