default_groups is defined as struct config_group **default_groups so
we don't need to allocate a whole struct but only enough space for a
pointer that points there.

(nab: Fix up minor apply breakage in for-next)
Signed-off-by: NSebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: NNicholas Bellinger <nab@linux-iscsi.org>