dt-bindings: hwmon: Add tmp75b to lm75.txt

Update the LM75's devicetree definition to allow Texas Instruments
TMP75B be probed.

Signed-off-by: Iker Perez del Palomar Sustatxa <iker.perez@codethink.co.uk>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>