m68k/mac: Add missing platform check before registering platform devices

On multi-platform kernels, the Mac platform devices should be registered
when running on Mac only. Else it may crash later.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: stable@vger.kernel.org

arch/m68k/mac/config.c

@@ -980,6 +980,9 @@ int __init mac_platform_init(void)
 {
 	u8 *swim_base;
 
+	if (!MACH_IS_MAC)
+		return -ENODEV;
+
 	/*
 	 * Serial devices
 	 */