Use variable in lcd_erase_line()

lcd_erase_line() is called with argument, but the argument is ignored by lcd_erase_line().

Marlin/ultralcd_implementation_hitachi_HD44780.h

 #if ENABLED(SHOW_BOOTSCREEN)
 
   void lcd_erase_line(int line) {
-    lcd.setCursor(0, 3);
+    lcd.setCursor(0, line);
     for (int i = 0; i < LCD_WIDTH; i++)
       lcd_print(' ');
   }