spi: qup: Convert ot let spi core handle checking transfer speed

Set master->max_speed_hz then spi core will handle checking transfer speed.
So we can remove the same checking in this driver.

Also remove checking spi->chip_select in spi_qup_setup(), the checking is done
by spi core.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Acked-by: Ivan T. Ivanov <iivanov@mm-sol.com>
Signed-off-by: Mark Brown <broonie@linaro.org>