Reduce set_homing_bump_feedrate, save 42 bytes (PR#2512)

Updates to `set_homing_bump_feedrate`:
- Move the string into Program Memory, reduce length by 31 bytes
- Use an auto to get the divisor, adjust it on error
- Set feedrate once, at the end

Marlin/Marlin_main.cpp

  */
 inline void set_homing_bump_feedrate(AxisEnum axis) {
   const int homing_bump_divisor[] = HOMING_BUMP_DIVISOR;
-  if (homing_bump_divisor[axis] >= 1)
-    feedrate = homing_feedrate[axis] / homing_bump_divisor[axis];
-  else {
-    feedrate = homing_feedrate[axis] / 10;
-    SERIAL_ECHOLN("Warning: The Homing Bump Feedrate Divisor cannot be less than 1");
+  int hbd = homing_bump_divisor[axis];
+  if (hbd < 1) {
+    hbd = 10;
+    SERIAL_ECHO_START;
+    SERIAL_ECHOLNPGM("Warning: Homing Bump Divisor < 1");
   }
+  feedrate = homing_feedrate[axis] / hbd;
 }
 inline void line_to_current_position() {
   plan_buffer_line(current_position[X_AXIS], current_position[Y_AXIS], current_position[Z_AXIS], current_position[E_AXIS], feedrate/60, active_extruder);