ALSA: mixer: oss: Add card disconnect checkpoints

In the Linux kernel, the following vulnerability has been resolved: ALSA: mixer: oss: Add card disconnect checkpoints ALSA OSS mixer layer calls the kcontrol ops rather individually, and pending calls might be not always caught at disconnecting the device. For avoiding the potential UAF scenarios, add sanity checks of the card disconnection at each entry point of OSS mixer accesses. The rwsem is taken just before that check, hence the rest context should be covered by that properly.