drivers/platform/x86/amilo-rfkill.c::amilo_rfkill_probe() avoid NULL deref

In drivers/platform/x86/amilo-rfkill.c::amilo_rfkill_probe() the call
to dmi_first_match() may fail and return NULL. If it does return NULL,
then we'll be dereferencing a NULL pointer in the rfkill_alloc() call
where we do 'system_id->driver_data' --> KABOOM!

Avoid that problem by testing for a NULL return value from
dmi_first_match() and bailing out if it fails.

I was a bit uncertain about what to return in the failure case. In the
end I settled for -ENXIO as the most logical error to return.
Signed-off-by: Jesper Juhl <jj@chaosbits.net>
Signed-off-by: Matthew Garrett <mjg@redhat.com>

drivers/platform/x86/amilo-rfkill.c

@@ -97,9 +97,12 @@ static struct rfkill *amilo_rfkill_dev;
 
 static int __devinit amilo_rfkill_probe(struct platform_device *device)
 {
+	int rc;
 	const struct dmi_system_id *system_id =
 		dmi_first_match(amilo_rfkill_id_table);
-	int rc;
+
+	if (!system_id)
+		return -ENXIO;
 
 	amilo_rfkill_dev = rfkill_alloc(KBUILD_MODNAME, &device->dev,
 					RFKILL_TYPE_WLAN,