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
diff --git a/arch/m68k/mac/config.c b/arch/m68k/mac/config.c
index 96fa6ed..d9f62e0 100644
--- a/arch/m68k/mac/config.c
+++ b/arch/m68k/mac/config.c
@@ -980,6 +980,9 @@
 {
 	u8 *swim_base;
 
+	if (!MACH_IS_MAC)
+		return -ENODEV;
+
 	/*
 	 * Serial devices
 	 */