fix I2C case where using different pins would not work with libs calling begin internally

if you call Wire.begin(new_sda, new_scl) and your library calls
internally Wire.begin() this will overwrite the SDA,SCL pins to the
default ones

libraries/Wire/Wire.cpp

@@ -55,6 +55,8 @@ TwoWire::TwoWire(){}
 // Public Methods //////////////////////////////////////////////////////////////
 
 void TwoWire::begin(int sda, int scl){
+  default_sda_pin = sda;
+  default_scl_pin = scl;
   twi_init(sda, scl);
   flush();
 }