ASoC: rockchip: pdm: change dma burst to 8

This patch is to avoid fifo xrun in some timing case.

Change-Id: I511ebc4c443f1c3369fff1c4b4eb5faf145d5ae5
Signed-off-by: Sugar Zhang <sugar.zhang@rock-chips.com>

sound/soc/rockchip/rockchip_pdm.c

@@ -24,7 +24,7 @@
 
 #include "rockchip_pdm.h"
 
-#define PDM_DMA_BURST_SIZE	(16) /* size * width: 16*4 = 64 bytes */
+#define PDM_DMA_BURST_SIZE	(8) /* size * width: 8*4 = 32 bytes */
 
 struct rk_pdm_dev {
 	struct device *dev;