i2c: cleanup i2c_register_adapter() by refactoring recovery init

Move recovery init to a seperate function to let have
i2c_register_adapter() less lines and to avoid goto and a label.
Refactor string handling there for consistency and to save some bytes.

Signed-off-by: Wolfram Sang <wsa-dev@sang-engineering.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>