watchdog: tqmx86: Fix a couple IS_ERR() vs NULL bugs

These functions return NULL on error but we accidentally check
for IS_ERR() instead.

Fixes: e3c21e08 ("watchdog: tqmx86: Add watchdog driver for the IO controller")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>