platform/chrome: wilco_ec: remove return value check of debugfs_create_dir()

Smatch complains that:
wilco_ec_debugfs_probe() warn: 'debug_info->dir' 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: Zhengkang Huang <zkhuang@hust.edu.cn>
Reviewed-by: Dongliang Mu <dzm91@hust.edu.cn>
Signed-off-by: Tzung-Bi Shih <tzungbi@kernel.org>
Link: https://lore.kernel.org/r/20230419100303.343379-1-zkhuang@hust.edu.cn