s390/sysinfo: add missing #ifdef CONFIG_PROC_FS

Get rid of this compile warning for !PROC_FS:

  CC      arch/s390/kernel/sysinfo.o
arch/s390/kernel/sysinfo.c:275:12: warning: 'sysinfo_show' defined but not used [-Wunused-function]
 static int sysinfo_show(struct seq_file *m, void *v)
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/kernel/sysinfo.c

@@ -59,6 +59,8 @@ int stsi(void *sysinfo, int fc, int sel1, int sel2)
 }
 EXPORT_SYMBOL(stsi);
 
+#ifdef CONFIG_PROC_FS
+
 static bool convert_ext_name(unsigned char encoding, char *name, size_t len)
 {
 	switch (encoding) {
@@ -301,6 +303,8 @@ static int __init sysinfo_create_proc(void)
 }
 device_initcall(sysinfo_create_proc);
 
+#endif /* CONFIG_PROC_FS */
+
 /*
  * Service levels interface.
  */