This fixes an invalid memory access when exiting the module:
exit_and_cleanup destroys the object, but lock_guard is destructed after
and accesses the lock.
- fixes the deadlock in px4io ioctl mixer reset
- px4io Run() locks (CDev semaphore)
- mixer load goes through px4io ioctl MIXERIOCRESET which calls MixingOutput::resetMixerThreadSafe()
- MixingOutput::resetMixerThreadSafe() stores a Command::Type::resetMixer command in an atomic variable, schedules a work queue cycle, then sleep spins until the command is cleared
- the execution of the cycle eventually calls back into PX4IO::updateOutputs(), which tries to lock (and waits forever)
henrykotze