Squish the code down a little

Marlin/Marlin_main.cpp

 
   if (axis == X_AXIS ? HOMEAXIS_DO(X) : axis == Y_AXIS ? HOMEAXIS_DO(Y) : axis == Z_AXIS ? HOMEAXIS_DO(Z) : 0) {
 
-    int axis_home_dir;
-
-    #ifdef DUAL_X_CARRIAGE
-      axis_home_dir = (axis == X_AXIS) ? x_home_dir(active_extruder) : home_dir(axis);
-    #else
-      axis_home_dir = home_dir(axis);
-    #endif
+    int axis_home_dir =
+      #ifdef DUAL_X_CARRIAGE
+        (axis == X_AXIS) ? x_home_dir(active_extruder) :
+      #endif
+      home_dir(axis);
 
     // Set the axis position as setup for the move
     current_position[axis] = 0;