drivers/base/cpu.c: fix the output from /sys/devices/system/cpu/offline

Without CONFIG_CPUMASK_OFFSTACK, simply inverting cpu_online_mask leads
to CPUs beyond nr_cpu_ids to be displayed twice and CPUs not even
possible to be displayed as offline.

Signed-off-by: Jan Beulich <[e-mail]>
Cc: Andi Kleen <[e-mail]>
Cc: Stephen Rothwell <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Cc: stable <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/base/cpu.c

···
 	/* display offline cpus < nr_cpu_ids */
 	if (!alloc_cpumask_var(&offline, GFP_KERNEL))
 		return -ENOMEM;
-	cpumask_complement(offline, cpu_online_mask);
+	cpumask_andnot(offline, cpu_possible_mask, cpu_online_mask);
 	n = cpulist_scnprintf(buf, len, offline);
 	free_cpumask_var(offline);