i2c: sirf: register i2c_client from dt child-nodes in probe entry

in probe() entry of i2c_driver, set the of node of adapter and
call of_i2c_register_devices to register all i2c_client from
dt child-nodes

Signed-off-by: Barry Song <Baohua.Song@csr.com>
Signed-off-by: Wolfram Sang <w.sang@pengutronix.de>