mbv: minor cleanup

mbv/apps/helloworld/helloworld.cc

@@ -1,12 +1,11 @@
 #include <cstdint>
 
+#include "gpio.h"
 #include "pol0.h"
 
-struct Gpio {
-    volatile uint32_t data;
-};
+namespace {
 
-#define gpio0 ((Gpio*)GPIO0_BASE)
+Gpio* gpio0;
 
 void sleep(int ms) {
     for (int m = 0; m < ms; m++) {
@@ -16,7 +15,10 @@ void sleep(int ms) {
     }
 }
 
+}  // namespace
+
 int main() {
+    gpio0 = Gpio::Instance(GPIO0_BASE);
     int out = 0;
 
     while (1) {