staging/vc04_services/bcm2835-camera: distinct numeration and names for devices

Create a static atomic counter for numerating cameras.
Use the Media Subsystem Kernel Internal API to create distinct
device-names, so that the camera-number (given by the counter)
matches the camera-name.
Co-developed-by: Kay Friedrich <kay.friedrich@fau.de>
Signed-off-by: Kay Friedrich <kay.friedrich@fau.de>
Signed-off-by: Michael Kupfer <michael.kupfer@fau.de>
Link: https://lore.kernel.org/r/20191206085432.19962-1-michael.kupfer@fau.deSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/vc04_services/bcm2835-camera/bcm2835-camera.c

@@ -60,6 +60,9 @@ MODULE_PARM_DESC(max_video_width, "Threshold for video mode");
 module_param(max_video_height, int, 0644);
 MODULE_PARM_DESC(max_video_height, "Threshold for video mode");
 
+/* camera instance counter */
+static atomic_t camera_instance = ATOMIC_INIT(0);
+
 /* global device data array */
 static struct bm2835_mmal_dev *gdev[MAX_BCM2835_CAMERAS];
 
@@ -1870,7 +1873,6 @@ static int bcm2835_mmal_probe(struct platform_device *pdev)
 
 		/* v4l2 core mutex used to protect all fops and v4l2 ioctls. */
 		mutex_init(&dev->mutex);
-		dev->camera_num = camera;
 		dev->max_width = resolutions[camera][0];
 		dev->max_height = resolutions[camera][1];
 
@@ -1886,8 +1888,9 @@ static int bcm2835_mmal_probe(struct platform_device *pdev)
 		dev->capture.fmt = &formats[3]; /* JPEG */
 
 		/* v4l device registration */
-		snprintf(dev->v4l2_dev.name, sizeof(dev->v4l2_dev.name),
-			 "%s", BM2835_MMAL_MODULE_NAME);
+		dev->camera_num = v4l2_device_set_name(&dev->v4l2_dev,
+						       BM2835_MMAL_MODULE_NAME,
+						       &camera_instance);
 		ret = v4l2_device_register(NULL, &dev->v4l2_dev);
 		if (ret) {
 			dev_err(&pdev->dev, "%s: could not register V4L2 device: %d\n",