s390/hvc_iucv: fix sparse warning

drivers/tty/hvc/hvc_iucv.c:131:25: warning: symbol 'hvc_iucv_get_private' was not
declared. Should it be static?
Signed-off-by: Hendrik Brueckner <brueckner@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

drivers/tty/hvc/hvc_iucv.c

@@ -126,7 +126,7 @@ static struct iucv_handler hvc_iucv_handler = {
  * This function returns the struct hvc_iucv_private instance that corresponds
  * to the HVC virtual terminal number specified as parameter @num.
  */
-struct hvc_iucv_private *hvc_iucv_get_private(uint32_t num)
+static struct hvc_iucv_private *hvc_iucv_get_private(uint32_t num)
 {
 	if ((num < HVC_IUCV_MAGIC) || (num - HVC_IUCV_MAGIC > hvc_iucv_devices))
 		return NULL;