hwmon: (sbtsi_temp) Fix Documenation kernel-doc warning

Fix Documentation/hwmon/ kernel-doc warning in 5.11-rc1:

lnx-511-rc1/Documentation/hwmon/sbtsi_temp.rst:4: WARNING: Title underline too short.

Kernel driver sbtsi_temp
==================

Fixes: 6ec3fcf5 ("hwmon: (sbtsi) Add documentation")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Kun Yi <kunyi@google.com>
Cc: Guenter Roeck <linux@roeck-us.net>
Cc: Jean Delvare <jdelvare@suse.com>
Cc: linux-hwmon@vger.kernel.org
Link: https://lore.kernel.org/r/20201229035428.31270-1-rdunlap@infradead.orgSigned-off-by: Guenter Roeck <linux@roeck-us.net>

Documentation/hwmon/sbtsi_temp.rst

 .. SPDX-License-Identifier: GPL-2.0-or-later
 
 Kernel driver sbtsi_temp
-==================
+========================
 
 Supported hardware: