dt-bindings: hwmon: ina2xx: Add label property

Add a label property to allow a custom name to be used for identifying
a device on the board. This is useful when multiple devices are present on
the same board. Similar change was done by commit ffae65fb
("dt-bindings: spi: spi-cadence: Add label property").

Signed-off-by: Michal Simek <michal.simek@amd.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/6f3c57d08984c1978569d3918cb38eb295c0c67d.1703077926.git.michal.simek@amd.com


Signed-off-by: Guenter Roeck <linux@roeck-us.net>