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