dt-bindings: hwmon: (lm90) Document ti,tmp451 compatible string

The TI TMP451 temperature sensors are compatible with the National LM90
temperature sensors.
Signed-off-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

Documentation/devicetree/bindings/hwmon/lm90.txt

@@ -23,6 +23,7 @@ Required node properties:
 		"onnn,nct1008"
 		"winbond,w83l771"
 		"nxp,sa56004"
+		"ti,tmp451"
 
 - reg: I2C bus address of the device