TTY: amiserial, add missing platform check

When booting a multi-platform m68k kernel on a non-Amiga with
"console=ttyS0" on the kernel command line, it crashes with:

Unable to handle kernel access at virtual address 81dff01c
Oops: 00000000
PC: [<001e09a8>] serial_console_write+0xc/0x70

Add the missing platform check to amiserial_console_init() to fix this.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/drivers/tty/amiserial.c b/drivers/tty/amiserial.c
index 2b86f8e..71630a2 100644
--- a/drivers/tty/amiserial.c
+++ b/drivers/tty/amiserial.c
@@ -1855,6 +1855,9 @@
  */
 static int __init amiserial_console_init(void)
 {
+	if (!MACH_IS_AMIGA)
+		return -ENODEV;
+
 	register_console(&sercons);
 	return 0;
 }