[ELEKTOR_F072C8] Update variant.cpp (stm32duino#922)

Removed entry of PA_3 for where PA_2 should be. Makes PA_2 now work

Author: lab-mathias-claussen

variants/ELEKTOR_F072C8/variant.cpp

@@ -66,7 +66,7 @@ const PinName digitalPin[] = {
   //Analog Pins
   PA_0,  //D27, A0
   PA_1,  //D28, A1
-  PA_3,  //D29, A2
+  PA_2,  //D29, A2
   PA_3,  //D30, A3
   PA_4,  //D31, A4
   PA_5,  //D32, A5