sky2: Remove redundant NULL check for debugfs_create_dir

Since debugfs_create_dir() returns ERR_PTR, IS_ERR() is enough to
check whether the directory is successfully created. So remove the
redundant NULL check.

Signed-off-by: Ruan Jinjie <ruanjinjie@huawei.com>
Reviewed-by: Leon Romanovsky <leonro@nvidia.com>
Link: https://lore.kernel.org/r/20230817073017.350002-1-ruanjinjie@huawei.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>