Fix HOMING_BACKOFF_MM for DELTA (#16657)

Marlin/src/module/delta.cpp

@@ -254,7 +254,7 @@ void home_delta() {
       - probe_offset.z
     #endif
   );
-  line_to_current_position(homing_feedrate(X_AXIS));
+  line_to_current_position(homing_feedrate(Z_AXIS));
   planner.synchronize();
 
   // Re-enable stealthChop if used. Disable diag1 pin on driver.
@@ -280,6 +280,14 @@ void home_delta() {
 
   sync_plan_position();
 
+  #if DISABLED(DELTA_HOME_TO_SAFE_ZONE) && defined(HOMING_BACKOFF_MM)
+    constexpr xyz_float_t endstop_backoff = HOMING_BACKOFF_MM;
+    if (endstop_backoff.z) {
+      current_position.z -= ABS(endstop_backoff.z) * Z_HOME_DIR;
+      line_to_current_position(homing_feedrate(Z_AXIS));
+    }
+  #endif
+
   if (DEBUGGING(LEVELING)) DEBUG_POS("<<< home_delta", current_position);
 }
 

Marlin/src/module/motion.cpp

@@ -1748,15 +1748,9 @@ void homeaxis(const AxisEnum axis) {
     if (axis == Z_AXIS && STOW_PROBE()) return;
   #endif
 
-  #ifdef HOMING_BACKOFF_MM
+  #if DISABLED(DELTA) && defined(HOMING_BACKOFF_MM)
     constexpr xyz_float_t endstop_backoff = HOMING_BACKOFF_MM;
-    const float backoff_mm = endstop_backoff[
+    const float backoff_mm = endstop_backoff[axis];
-      #if ENABLED(DELTA)
-        Z_AXIS
-      #else
-        axis
-      #endif
-    ];
     if (backoff_mm) {
       current_position[axis] -= ABS(backoff_mm) * axis_home_dir;
       line_to_current_position(