iwlwifi: mvm: fix aux station leak

When mvm is initialized we alloc aux station with aux queue.
We later free the station memory when driver is stopped, but we
never free the queue's memory, which casues a leak.

Add a proper de-initialization of the station.

Signed-off-by: Sharon <sara.sharon@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Link: https://lore.kernel.org/r/iwlwifi.20200529092401.0121c5be55e9.Id7516fbb3482131d0c9dfb51ff20b226617ddb49@changeid