i2c: tegra: use i2c_timings for bus clock freq

Use i2c_timings struct and corresponding methods to get bus clock frequency

Signed-off-by: Akhil R <akhilrajeev@nvidia.com>
Suggested-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Reviewed-by: Dmitry Osipenko <digetx@gmail.com>
Tested-by: Dmitry Osipenko <digetx@gmail.com>
Signed-off-by: Wolfram Sang <wsa@kernel.org>