s390/cpuinfo: fix wrong output when CPU0 is offline

/proc/cpuinfo should not print information about CPU 0 when it is offline.

Fixes: 281eaa8c ("s390/cpuinfo: simplify locking and skip offline cpus early")
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>
Reviewed-by: Heiko Carstens <heiko.carstens@de.ibm.com>
[heiko.carstens@de.ibm.com: shortened commit message]
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

arch/s390/kernel/processor.c

@@ -188,8 +188,9 @@ static void show_cpu_mhz(struct seq_file *m, unsigned long n)
 static int show_cpuinfo(struct seq_file *m, void *v)
 {
 	unsigned long n = (unsigned long) v - 1;
+	unsigned long first = cpumask_first(cpu_online_mask);
 
-	if (!n)
+	if (n == first)
 		show_cpu_summary(m, v);
 	if (!machine_has_cpu_mhz)
 		return 0;
@@ -204,6 +205,8 @@ static inline void *c_update(loff_t *pos)
 {
 	if (*pos)
 		*pos = cpumask_next(*pos - 1, cpu_online_mask);
+	else
+		*pos = cpumask_first(cpu_online_mask);
 	return *pos < nr_cpu_ids ? (void *)*pos + 1 : NULL;
 }