[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/drivers/s390/char/ctrlchar.c b/drivers/s390/char/ctrlchar.c
index 0ea6f36..d83eb63 100644
--- a/drivers/s390/char/ctrlchar.c
+++ b/drivers/s390/char/ctrlchar.c
@@ -23,7 +23,7 @@
 	handle_sysrq(ctrlchar_sysrq_key, NULL, (struct tty_struct *) tty);
 }
 
-static DECLARE_WORK(ctrlchar_work, ctrlchar_handle_sysrq, 0);
+static DECLARE_WORK(ctrlchar_work, ctrlchar_handle_sysrq, NULL);
 #endif