#5 only set I2C_BUFFER_LENGTH if not already defined, this fixes compile warnings on ESP32

Author: trycoon

src/SparkFun_Ublox_Arduino_Library.h

@@ -62,10 +62,9 @@
 //#elif __MK20DX256__
 //Teensy
 
-//#elif ARDUINO_ARCH_ESP32
-//ESP32 based platforms
+#endif
 
-#else
+#ifndef I2C_BUFFER_LENGTH
 
 //The catch-all default is 32
 #define I2C_BUFFER_LENGTH 32
@@ -369,3 +368,4 @@ class SFE_UBLOX_GPS
 };
 
 #endif
+