TTY: tty_alloc_driver() returns error pointers

We changed these from alloc_tty_driver() to tty_alloc_driver() so the
error handling needs to modified to check for IS_ERR() instead of NULL.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/drivers/char/ttyprintk.c b/drivers/char/ttyprintk.c
index 561f8aa..af98f6d 100644
--- a/drivers/char/ttyprintk.c
+++ b/drivers/char/ttyprintk.c
@@ -187,8 +187,8 @@
 			TTY_DRIVER_RESET_TERMIOS |
 			TTY_DRIVER_REAL_RAW |
 			TTY_DRIVER_UNNUMBERED_NODE);
-	if (!ttyprintk_driver)
-		return ret;
+	if (IS_ERR(ttyprintk_driver))
+		return PTR_ERR(ttyprintk_driver);
 
 	ttyprintk_driver->driver_name = "ttyprintk";
 	ttyprintk_driver->name = "ttyprintk";