hid: roccat-savu: convert class code to use bin_attrs in groups

Now that attribute groups support binary attributes, use them instead of
the dev_bin_attrs field in struct class, as that is going away soon.

Cc: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>