spi: spi-ep93xx: don't bother calculating the divisors in ep93xx_spi_setup()

The divisors needed to generate the SPI clock are calculated per
transfer based on the t->speed_hz. There is no reason to calculate
them in ep93xx_spi_setup().

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Acked-by: Mika Westerberg <mika.westerberg@iki.fi>
Signed-off-by: Mark Brown <broonie@linaro.org>