[S390] Fix sparse warnings.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
diff --git a/arch/s390/mm/cmm.c b/arch/s390/mm/cmm.c
index 81be2fe..ceea51c 100644
--- a/arch/s390/mm/cmm.c
+++ b/arch/s390/mm/cmm.c
@@ -161,7 +161,7 @@
 static void
 cmm_start_thread(void)
 {
-	kernel_thread(cmm_thread, 0, 0);
+	kernel_thread(cmm_thread, NULL, 0);
 }
 
 static void