powerpc/powernv: Fix CPU_HOTPLUG=n idle.c compile error

commit 67d20418 upstream.

Fixes: a7cd88da ("powerpc/powernv: Move CPU-Offline idle state invocation from smp.c to idle.c")
Cc: Gautham R. Shenoy <ego@linux.vnet.ibm.com>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Acked-by: Gautham R. Shenoy <ego@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>