darwin: add missing locking around cached device list cleanup

The cleanup function darwin_cleanup_devices was intented to be called only once
at program exit. When the initialization/finalization code was changed to
destroy the cached device list on last exit this function should have been
modified to require a lock on darwin_cached_devices_lock. This commit updates
cleanup to protect the cached device list with the cached devices mutex and
updates darwin_init to print out an error and return if a reference leak is

Also using this opportunity to correct the naming of the mutex. Changed
darwin_cached_devices_lock to darwin_cached_devices_mutex. Also cleaning the
initialization code up a bit. Removing the context pointer from the hotplug
thread as it is not used for anything but logging.

Fixes #1124

Signed-off-by: Nathan Hjelm <hjelmn@google.com>
2 files changed