fixed error in some of the Con functions where wrong unit was used

src/main/c/main_taschenrechner.c

@@ -448,11 +448,11 @@ double ConSpeed(double speed, int startingUnit, int endingUnit) {
         switch (endingUnit)
         {
         case 0: //kmh to kmh
-            return distance;
+            return speed;
             break;
 
         case 1: //kmh to mph
-            return distance * 0.621371;
+            return speed * 0.621371;
             break;
 
         default:
@@ -463,11 +463,11 @@ double ConSpeed(double speed, int startingUnit, int endingUnit) {
         switch (endingUnit)
         {
         case 0: //mph to kmh
-            return distance * 1.60934;
+            return speed * 1.60934;
             break;
 
         case 1: //mph to mph
-            return distance;
+            return speed;
             break;
 
         default: