sparc64: vcc: Check for IS_ERR() instead of NULL

The tty_alloc_driver() function never returns NULL, it returns error
pointers on error.

Fixes: ce808b746325 ("sparc64: vcc: TTY driver initialization and cleanup")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/tty/vcc.c b/drivers/tty/vcc.c
index 5e608173..7167291 100644
--- a/drivers/tty/vcc.c
+++ b/drivers/tty/vcc.c
@@ -1086,9 +1086,9 @@
 	pr_info("VCC: %s\n", version);
 
 	vcc_tty_driver = tty_alloc_driver(VCC_MAX_PORTS, VCC_TTY_FLAGS);
-	if (!vcc_tty_driver) {
+	if (IS_ERR(vcc_tty_driver)) {
 		pr_err("VCC: TTY driver alloc failed\n");
-		return -ENOMEM;
+		return PTR_ERR(vcc_tty_driver);
 	}
 
 	vcc_tty_driver->driver_name = vcc_driver_name;