iwlwifi: mvm: clear firmware running bit earlier

Clear the firmware running bit before flushing the FW (error) dump
work, because otherwise debugfs isn't blocked (previous patch) and
can cause a new work to be scheduled, which will then run after we
actually shut down the device, wreaking havoc. Clearing it ensures
that debugfs can't interfere anymore, and we can safely cancel or
flush the work struct.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>