[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/include/asm-s390/ccwdev.h b/include/asm-s390/ccwdev.h
index 12456cb..58c70ac 100644
--- a/include/asm-s390/ccwdev.h
+++ b/include/asm-s390/ccwdev.h
@@ -63,7 +63,7 @@
 		return id;
 	}
 
-	return 0;
+	return NULL;
 }
 
 /* The struct ccw device is our replacement for the globally accessible