[S390] avoid default_llseek in s390 drivers

Use nonseekable_open for a couple of s390 device drivers. This avoids
the use of default_llseek function which has a dependency on the BKL.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
diff --git a/drivers/s390/cio/css.c b/drivers/s390/cio/css.c
index da6df04..ac94ac75 100644
--- a/drivers/s390/cio/css.c
+++ b/drivers/s390/cio/css.c
@@ -1065,6 +1065,7 @@
 }
 
 static const struct file_operations cio_settle_proc_fops = {
+	.open = nonseekable_open,
 	.write = cio_settle_write,
 };