Fixes BLE data printing (#7699)

* Fixes BLE data printing

BLE data has no '\0' terminator, therefore it can't be printed as a regular C string.
This fix just prints the BLE data based on its length.

* Simplify printing to a single call

libraries/BLE/examples/BLE_client/BLE_client.ino

@@ -29,7 +29,8 @@ static void notifyCallback(
     Serial.print(" of data length ");
     Serial.println(length);
     Serial.print("data: ");
-    Serial.println((char*)pData);
+    Serial.write(pData, length);
+    Serial.println();
 }
 
 class MyClientCallback : public BLEClientCallbacks {