Instead of using custom variables and parser, convert the driver to use
the ones provided by I2C core.

No functional change intended.
Signed-off-by: NAndy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: NLudovic Desroches <ludovic.desroches@microchip.com>
Signed-off-by: NWolfram Sang <wsa@the-dreams.de>