staging: lustre: unwrap some ldebugfs_register() calls

staging: lustre: unwrap some ldebugfs_register() calls

When the third option (list) to ldebugfs_register() is NULL, it's the
same as just calling debugfs_create_dir().  So unwind this and call
debugfs_create_dir() directly.

This ends up saving lots of code as we do not need to do any error
checking of the return value (because it does not matter).

The ldebugfs_register() call will be removed in a later patch when it is
fully removed, right now there are 2 outstanding users of it in the
tree.

Cc: Oleg Drokin <oleg.drokin@intel.com>
Cc: Andreas Dilger <andreas.dilger@intel.com>
Cc: James Simmons <jsimmons@infradead.org>
Cc: NeilBrown <neilb@suse.com>
Cc: Aastha Gupta <aastha.gupta4104@gmail.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Quentin Bouget <quentin.bouget@cea.fr>
Cc: Patrick Farrell <paf@cray.com>
Cc: Aliaksei Karaliou <akaraliou.dev@gmail.com>
Cc: "John L. Hammond" <john.hammond@intel.com>
Cc: Mathias Rav <mathiasrav@gmail.com>
Cc: Andriy Skulysh <andriy.skulysh@seagate.com>
Cc: Ben Evans <bevans@cray.com>
Cc: Bob Glosman <bob.glossman@intel.com>
Cc: lustre-devel@lists.lustre.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>