HID: magicmouse: fix NULL-deref on disconnect

Commit 9d7b186 ("HID: magicmouse: add support for Apple Magic
Trackpad 2") added a sanity check for an Apple trackpad but returned
success instead of -ENODEV when the check failed. This means that the
remove callback will dereference the never-initialised driver data
pointer when the driver is later unbound (e.g. on USB disconnect).

Reported-by: syzbot+ee6f6e2e68886ca256a8@syzkaller.appspotmail.com
Fixes: 9d7b186 ("HID: magicmouse: add support for Apple Magic Trackpad 2")
Cc: stable@vger.kernel.org      # 4.20
Cc: Claudio Mettler <claudio@ponyfleisch.ch>
Cc: Marek Wyborski <marek.wyborski@emwesoft.com>
Cc: Sean O'Brien <seobrien@chromium.org>
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

drivers/hid/hid-magicmouse.c

@@ -693,7 +693,7 @@ static int magicmouse_probe(struct hid_device *hdev,
 	if (id->vendor == USB_VENDOR_ID_APPLE &&
 	    id->product == USB_DEVICE_ID_APPLE_MAGICTRACKPAD2 &&
 	    hdev->type != HID_TYPE_USBMOUSE)
-		return 0;
+		return -ENODEV;
 
 	msc = devm_kzalloc(&hdev->dev, sizeof(*msc), GFP_KERNEL);
 	if (msc == NULL) {