wifi: mac80211: remove return value check of debugfs_create_dir()

wifi: mac80211: remove return value check of debugfs_create_dir()

Smatch complains that:
debugfs_hw_add() warn: 'statsd' is an error pointer or valid

Debugfs checks are generally not supposed to be checked for errors
and it is not necessary here.

Just delete the dead code.

Signed-off-by: Yingsha Xu <ysxu@hust.edu.cn>
Reviewed-by: Dongliang Mu <dzm91@hust.edu.cn>
Link: https://lore.kernel.org/r/20230419104548.30124-1-ysxu@hust.edu.cn
Signed-off-by: Johannes Berg <johannes.berg@intel.com>