mcb: Acquire reference to device in probe

mcb_probe() does not aqcuire a reference to the probed device but drops one
when removing the device. As it is actually using the device, it should grab
a reference via get_device().

This could lead to a panic found with a rmmod/modprobe stress test

Signed-off-by: Johannes Thumshirn <jthumshirn@suse.de>
Reported-by: Andreas Werner <andreas.werner@men.de>
Tested-by: Andreas Werner <andreas.werner@men.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/mcb/mcb-core.c

@@ -66,6 +66,7 @@ static int mcb_probe(struct device *dev)
 	if (!found_id)
 		return -ENODEV;
 
+	get_device(dev);
 	return mdrv->probe(mdev, found_id);
 }