dt: Add vendor prefix for Sensirion

Sensirion is a sensor manufacturer, providing relative humidity sensors,
temperature sensor and flow sensor solutions.

Signed-off-by: Marco Franchi <marco.franchi@nxp.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>