i2c: designware: Call i2c_dw_clk_rate() only once in i2c_dw_init_master()

i2c: designware: Call i2c_dw_clk_rate() only once in i2c_dw_init_master()

This is rather readability update than micro-optimization, or if not
optimization at all. We take the input clock rate to a variable and pass
that to SCL timing parameter calculation functions.

Reviewed-by: Andy Shevchenko <[email protected]>
Signed-off-by: Jarkko Nikula <[email protected]>
Signed-off-by: Wolfram Sang <[email protected]>