wmr: fix open_device_idx for macOS and multiple WMR headsets

We can't use findEndPoint because the macOS device path does not contain
a string representation of the interface number. But since there is only
a single HoloLens Sensors HID device per WMR headset, we don't have to
check the endpoint number. While at it, fix the device index handling in
case there are multiple WMR headsets attached.

src/drv_wmr/wmr.c

@@ -178,7 +178,7 @@ static hid_device* open_device_idx(int manufacturer, int product, int iface, int
 	while (cur_dev) {
 		printf("%04x:%04x %s\n", manufacturer, product, cur_dev->path);
 
-		if(findEndPoint(cur_dev->path, device_index) > 0 && iface == iface_cur){
+		if(idx == device_index && iface == iface_cur){
 			ret = hid_open_path(cur_dev->path);
 			printf("opening\n");
 		}
@@ -294,8 +294,10 @@ static ohmd_device* open_device(ohmd_driver* driver, ohmd_device_desc* desc)
 
 	priv->base.ctx = driver->ctx;
 
+	int idx = atoi(desc->path);
+
 	// Open the HMD device
-	priv->hmd_imu = open_device_idx(MICROSOFT_VID, HOLOLENS_SENSORS_PID, 0, 0, 2);
+	priv->hmd_imu = open_device_idx(MICROSOFT_VID, HOLOLENS_SENSORS_PID, 0, 1, idx);
 
 	if(!priv->hmd_imu)
 		goto cleanup;