bcache: 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 bcache sysfs code to use default_groups field which has
been the preferred way since aa30f47cf6 ("kobject: Add support for
default attribute groups to kobj_type") so that we can soon get rid of
the obsolete default_attrs field.

Cc: Kent Overstreet <kent.overstreet@gmail.com>
Cc: linux-bcache@vger.kernel.org
Acked-by: Coly Li <colyli@suse.de>
Link: https://lore.kernel.org/r/20220106100004.3277439-1-gregkh@linuxfoundation.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/md/bcache/sysfs.h

@@ -9,7 +9,7 @@ struct kobj_type type ## _ktype = {					\
 		.show	= type ## _show,				\
 		.store	= type ## _store				\
 	}),								\
-	.default_attrs	= type ## _files				\
+	.default_groups	= type ## _groups				\
 }
 
 #define SHOW(fn)							\