[PATCH] powerpc: Fix typo in topology.h

The fix to topology.h (5cfccd7f) seems to have
a typeo, struct sched_domain has an idle_idx member but not an idle_id
member. I assume this is the fix.

Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Paul Mackerras <paulus@samba.org>