ubifs: use default_groups in kobj_type

ubifs: use default_groups in kobj_type

There are currently 2 ways to create a set of sysfs files for a
kobj_type, through the default_attrs field, and the default_groups
field.  Move the ubifs sysfs code to use default_groups field which has
been the preferred way since aa30f47cf666 ("kobject: Add support for
default attribute groups to kobj_type") so that we can soon get rid of
the obsolete default_attrs field.

Cc: Stefan Schaeckeler <schaecsn@gmx.net>
Cc: linux-mtd@lists.infradead.org
Acked-by: Richard Weinberger <richard@nod.at>
Link: https://lore.kernel.org/r/20220114104820.1340879-1-gregkh@linuxfoundation.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>