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: NBrad Boyer <flar@allandria.com>
Signed-off-by: NGeert Uytterhoeven <geert@linux-m68k.org>

drivers/video/console/fbcon.c

@@ -3455,7 +3455,8 @@ static void fbcon_exit(void)
 		return;
 
 #ifdef CONFIG_ATARI
-	free_irq(IRQ_AUTO_4, fb_vbl_handler);
+	if (MACH_IS_ATARI)
+		free_irq(IRQ_AUTO_4, fb_vbl_handler);
 #endif
 
 	kfree((void *)softback_buf);