HID: magicmouse: Don't report REL_{X,Y} for Magic Trackpad

With the recent switch to having the hid layer handle standard axis
initialization, the Magic Trackpad now reports relative axes. This would
be fine in the normal mode, but the driver puts the device in multitouch
mode where no relative events are generated. Also, userspace software
depends on accurate axis information for device type detection. Thus,
ignoring the relative axes from the Magic Trackpad is best.
Signed-off-by: NChase Douglas <chase.douglas@canonical.com>
Signed-off-by: NJiri Kosina <jkosina@suse.cz>

drivers/hid/hid-magicmouse.c

@@ -433,6 +433,11 @@ static int magicmouse_input_mapping(struct hid_device *hdev,
 	if (!msc->input)
 		msc->input = hi->input;
 
+	/* Magic Trackpad does not give relative data after switching to MT */
+	if (hi->input->id.product == USB_DEVICE_ID_APPLE_MAGICTRACKPAD &&
+	    field->flags & HID_MAIN_ITEM_RELATIVE)
+		return -1;
+
 	return 0;
 }