md: 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 md rdev sysfs code to use default_groups field which
has been the preferred way since commit
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: Song Liu <song@kernel.org>
Cc: linux-raid@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Song Liu <song@kernel.org>