pds_core: fix debugfs_lookup dentry leak and error handling

In the Linux kernel, the following vulnerability has been resolved: pds_core: fix debugfs_lookup dentry leak and error handling debugfs_lookup() returns a dentry with an elevated reference count that must be released with dput(). The current code discards the returned dentry without calling dput(), causing a reference leak on every firmware reset recovery. Additionally, when CONFIG_DEBUG_FS is disabled, debugfs_lookup() returns ERR_PTR(-ENODEV), not NULL. The current check passes for error pointers and would call dput() on an invalid pointer, causing a crash.