spi/s3c64xx: Fix non-dmaengine usage

The multiplatform conversion in commit 788437 (spi: s3c64xx: move to
generic dmaengine API) tested for the use of the Samsung-specific DMA
API with SAMSUNG_DMADEV when in fact S3C_DMA should be used. This
renderd DMA based transfers non-functional on platforms not using
dmaengine.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>