iwlwifi: mvm: init drv_stats_lock

Otherwise lockdep complains about the lock, I'm not sure
why we didn't see this before.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>

diff --cc drivers/net/wireless/iwlwifi/mvm/debugfs.c
Simple merge