i2c: core: call of_i2c_setup_smbus_alert in i2c_register_adapter

Add a call to of_i2c_setup_smbus_alert when a i2c adapter is registered
so the the smbalert driver can be registered.

Signed-off-by: Phil Reid <preid@electromag.com.au>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>