fbcon: Protect free_irq() by MACH_IS_ATARI check

Add missing check for Atari in free_irq() call, which could cause problems on
multi-platform m68k kernels.
Reported-by: Brad Boyer <flar@allandria.com>
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>

drivers/video/console/fbcon.c

@@ -3455,6 +3455,7 @@ static void fbcon_exit(void)
 		return;
 
 #ifdef CONFIG_ATARI
+	if (MACH_IS_ATARI)
 		free_irq(IRQ_AUTO_4, fb_vbl_handler);
 #endif