Print::write not on RBL

It seems like this functionality got removed in the RBL SDK.
Add condition for compiler target..

SPP.h

@@ -120,7 +120,9 @@ public:
          */
         size_t write(const uint8_t* data, size_t size);
         /** Pull in write(const char *str) from Print */
+#if !defined(RBL_NRF51822)
         using Print::write;
+#endif
 #else
         /**
          * Writes the byte to send to a buffer. The message is send when either send() or after Usb.Task() is called.