s390/vmlogrdr: fix array access in vmlogrdr_open()

Fix check within vmlogrdr_open() if the minor address is not larger
than the number of array elements.

Found with "smatch":

drivers/s390/char/vmlogrdr.c:318 vmlogrdr_open() warn:
  buffer overflow 'sys_ser' 3 <= 3

Acked-by: Stefan Weinhuber <wein@de.ibm.com>
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/vmlogrdr.c b/drivers/s390/char/vmlogrdr.c
index 9b3a24e..cf31d33 100644
--- a/drivers/s390/char/vmlogrdr.c
+++ b/drivers/s390/char/vmlogrdr.c
@@ -313,7 +313,7 @@
 	int ret;
 
 	dev_num = iminor(inode);
-	if (dev_num > MAXMINOR)
+	if (dev_num >= MAXMINOR)
 		return -ENODEV;
 	logptr = &sys_ser[dev_num];