Fix Print::printf implementation

Author: tsl0922

cores/nRF5/Print.cpp

@@ -22,6 +22,7 @@
 #include <string.h>
 #include <math.h>
 #include "Arduino.h"
+#include "printf.h"
 
 #include "Print.h"
 
@@ -187,11 +188,16 @@ size_t Print::println(const Printable& x)
   return n;
 }
 
+extern "C" void streamOutput(char character, void* arg)
+{
+  (static_cast<Print *>(arg))->write(character);
+}
+
 int Print::printf(const char* format, ...)
 {
   va_list va;
   va_start(va, format);
-  int ret = vprintf(format, va);
+  int ret = vfctprintf(&streamOutput, this, format, va);
   va_end(va);
   return ret;
 }