i2c: designware_i2c: Drop scl_sda_cfg parameter

Instead of passing this parameter into __dw_i2c_set_bus_speed(), pass in
the driver's private data, from which the function can obtain that
information. This allows the function to have access to the full state of
the driver.

Signed-off-by: Sicomp_param1mon Glass <sjg@chromium.org>
Reviewed-by: Heiko Schocher <hs@denx.de>
Signed-off-by: Simon Glass <sjg@chromium.org>