Make top and bottom border lines match.

Documentation/hwmon/sht4x.rst:42: WARNING: Malformed table.
Text in column margin in table line 4.

Fixes: 505c2549 ("hwmon: Add sht4x Temperature and Humidity Sensor Driver")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Navin Sankar Velliangiri <navin@linumiz.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/20210727232054.7426-1-rdunlap@infradead.orgSigned-off-by: Guenter Roeck <linux@roeck-us.net>