spi: s3c64xx: fix casting warning

sdd->ops->request is unsigned int, not unsigned long.
Also, sdd->rx_dma.ch is a 'struct dma_chan *'.
Thus, (void *) is converted to (struct dma_chan *)(unsigned long),
in order to fix possible sparse warnings.

Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Signed-off-by: Mark Brown <broonie@linaro.org>