i2c: designware: Adjust bus speed independently of ACPI

John Stultz reported that commit f9288fcc ("i2c: designware: Move
ACPI parts into common module") caused a regression on the HiKey board
where adv7511 HDMI bridge driver wasn't probing anymore due the I2C bus
failed to start.

It seems the change caused the bus speed being zero when CONFIG_ACPI
not set and neither speed based on "clock-frequency" device property
or default fast mode is set.

Fix this by splitting i2c_dw_acpi_adjust_bus_speed() to
i2c_dw_acpi_round_bus_speed() and i2c_dw_adjust_bus_speed(), where
the latter one has the code that runs independently of ACPI.

Fixes: f9288fcc ("i2c: designware: Move ACPI parts into common module")
Reported-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
Tested-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Wolfram Sang <wsa@kernel.org>