i2c: qcom-cci: don't put a device tree node before i2c_add_adapter()

There is a minor chance for a race, if a pointer to an i2c-bus subnode
is stored and then reused after releasing its reference, and it would
be sufficient to get one more reference under a loop over children
subnodes.

Fixes: e5175261 ("i2c: Add Qualcomm CCI I2C driver")
Signed-off-by: Vladimir Zapolskiy <vladimir.zapolskiy@linaro.org>