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/tty/moxa.c b/drivers/tty/moxa.c
index 3b17a04..56e616b 100644
--- a/drivers/tty/moxa.c
+++ b/drivers/tty/moxa.c
@@ -1048,8 +1048,8 @@
 	moxaDriver = tty_alloc_driver(MAX_PORTS + 1,
 			TTY_DRIVER_REAL_RAW |
 			TTY_DRIVER_DYNAMIC_DEV);
-	if (!moxaDriver)
-		return -ENOMEM;
+	if (IS_ERR(moxaDriver))
+		return PTR_ERR(moxaDriver);
 
 	moxaDriver->name = "ttyMX";
 	moxaDriver->major = ttymajor;