spi: topcliff-pch: Convert to use master->max_speed_hz

Set "master->max_speed_hz = PCH_MAX_BAUDRATE" then we can remove pch_spi_setup.
In additional, pspi->max_speed_hz will never be 0 because it's default value
will be set to master->max_speed_hz.

Also remove list_empty checking in pch_spi_transfer() because the checking is
done by spi core.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Signed-off-by: Mark Brown <broonie@linaro.org>