pds_core: Remove redundant null pointer checks

Since the debugfs_create_dir() never returns a null pointer, checking
the return value for a null pointer is redundant, and using IS_ERR is
safe enough.

Signed-off-by: Li Zetao <lizetao1@huawei.com>
Link: https://patch.msgid.link/20240903143343.2004652-1-lizetao1@huawei.com


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