Nobody (including me) noticed that these functions were exported but not
added to the header :/

Fixes: 7159dbda ("i2c: core: improve return value handling of i2c_new_device and i2c_new_dummy")
Signed-off-by: NWolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: NBartosz Golaszewski <bgolaszewski@baylibre.com>
Reviewed-by: NKieran Bingham <kieran.bingham+renesas@ideasonboard.com>
Signed-off-by: NWolfram Sang <wsa@the-dreams.de>