Remove unused variable fan_rot

and satisfy the compiler about the implicit compare.

Marlin/dogm_lcd_implementation.h

@@ -256,9 +256,6 @@ static void _draw_heater_status(int x, int heater) {
 }
 
 static void lcd_implementation_status_screen() {
-
-  static unsigned char fan_rot = 0;
- 
   u8g.setColorIndex(1); // black on white
 
   // Symbols menu graphics, animated fan
@@ -485,7 +482,7 @@ static void _drawmenu_sd(bool isSelected, uint8_t row, const char* pstr, const c
   lcd_implementation_mark_as_selected(row, isSelected);
 
   if (isDir) lcd_print(LCD_STR_FOLDER[0]);
-  while (c = *filename) {
+  while ((c = *filename)) {
     n -= lcd_print(c);
     filename++;
   }