navio_adc: add override flag to init

Signed-off-by: Nicolae Rosia <nicolae.rosia@gmail.com>

src/drivers/navio_adc/navio_adc.cpp

@@ -81,7 +81,7 @@ public:
 	NavioADC();
 	virtual ~NavioADC();
 
-	virtual int init();
+	virtual int init() override;
 
 	virtual ssize_t devRead(void *buf, size_t count) override;
 	virtual int devIOCTL(unsigned long request, unsigned long arg) override;