hwmon: docs: Extend inspur-ipsps1 title underline

Sphinx is generating a build warning as the title underline
of this file is too short.
Signed-off-by: Adam Zerella <adam.zerella@gmail.com>
Reviewed-by: Jean Delvare <jdelvare@suse.de>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

Documentation/hwmon/inspur-ipsps1.rst

 Kernel driver inspur-ipsps1
-=======================
+===========================
 
 Supported chips: