i2c: arb-gpio-challenge: use of_get_i2c_adapter_by_node interface

This change is needed to properly lock I2C parent bus driver.

Prior to this change i2c_put_adapter() is misused, which may lead
to an overflow over zero of I2C bus driver user counter.

Signed-off-by: Vladimir Zapolskiy <vladimir_zapolskiy@mentor.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>