i2c: designware-pci: no need to provide clk_khz

The clk_khz field makes sense only if SS counters are not provided. Since we
provide them for Haswell and Baytrail explicitly we may omit the clk_khz
parameter.

Reviewed-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>