iwlwifi: turn on a lockdep assertion

CMD_SYNC is zero so the if (cmd->flags & CMD_SYNC) is never true and we
never check the assertion.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>