spi: s3c64xx: add missing check for polling mode

Due to changes in mainline prior to submission the spi device detection
in polling mode breaks. This revealed the missing check for polling
during dma prepare. This patch adds the missing check.
Signed-off-by: Girish K S <ks.giri@samsung.com>
Signed-off-by: Mark Brown <broonie@linaro.org>

drivers/spi/spi-s3c64xx.c

@@ -434,6 +434,9 @@ static int s3c64xx_spi_prepare_transfer(struct spi_master *spi)
 	dma_cap_mask_t mask;
 	int ret;
 
+	if (is_polling(sdd))
+		return 0;
+
 	dma_cap_zero(mask);
 	dma_cap_set(DMA_SLAVE, mask);