spi: coldfire-qspi: Simplify the code to set register bits for transfer speed

spi core will use spi->max_speed_hz as transfer speed if the transfer speed was
not set. So we don't need to test t->speed_hz in mcfqspi_transfer_one().

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