Fix some remainings ARMCC warnings

Author: Donatien Garnier

features/nfc/nfc/NFCController.h

@@ -163,7 +163,7 @@ class NFCController : private NFCControllerDriver::Delegate {
     static void s_polling_callback(nfc_transceiver_t *pTransceiver, nfc_err_t ret, void *pUserData);
 
     // Implementation of NFCControllerDriver::Delegate
-    void on_hw_interrupt();
+    virtual void on_hw_interrupt();
 
     // Triggers when scheduler must be run again
     void on_timeout();

features/nfc/source/nfc/NFCEEPROM.cpp

@@ -422,4 +422,4 @@ void NFCEEPROM::handle_error(nfc_err_t ret)
 NFCNDEFCapable::Delegate *NFCEEPROM::ndef_capable_delegate()
 {
     return _delegate;
-}
+}

features/nfc/source/nfc/NFCNDEFCapable.cpp

@@ -82,4 +82,4 @@ ndef_msg_t *NFCNDEFCapable::ndef_message()
 NFCNDEFCapable::Delegate *NFCNDEFCapable::ndef_capable_delegate()
 {
     return NULL;
-}
+}