staging: bcm2835-camera: Abort probe if there is no camera

Abort the probing of the camera driver in case there isn't a camera
actually connected to the Raspberry Pi. This solution also avoids a
NULL ptr dereference of mmal instance on driver unload.

Fixes: 7b3ad5abf0 ("staging: Import the BCM2835 MMAL-based V4L2 camera driver.")
Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
Reviewed-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Reviewed-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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

@@ -1841,6 +1841,12 @@ static int bcm2835_mmal_probe(struct platform_device *pdev)
 	num_cameras = get_num_cameras(instance,
 				      resolutions,
 				      MAX_BCM2835_CAMERAS);
+
+	if (num_cameras < 1) {
+		ret = -ENODEV;
+		goto cleanup_mmal;
+	}
+
 	if (num_cameras > MAX_BCM2835_CAMERAS)
 		num_cameras = MAX_BCM2835_CAMERAS;
 
@@ -1940,6 +1946,9 @@ cleanup_gdev:
 	pr_info("%s: error %d while loading driver\n",
 		BM2835_MMAL_MODULE_NAME, ret);
 
+cleanup_mmal:
+	vchiq_mmal_finalise(instance);
+
 	return ret;
 }