mmc: dw_mmc: initialize zero for dma_slave_config

This fixes uninitialized variable introduced by commit ddd2e87
("dmaengine: pl330: add support for interlace size config")

Change-Id: Ib1bbec21053fbcccf85a339d8ed7eec0bbe77727
Signed-off-by: Sugar Zhang <sugar.zhang@rock-chips.com>

Author: Sugar Zhang

drivers/mmc/host/dw_mmc.c

@@ -748,6 +748,7 @@ static int dw_mci_edmac_start_dma(struct dw_mci *host,
 	int ret = 0;
 
 	/* Set external dma config: burst size, burst width */
+	memset(&cfg, 0, sizeof(cfg));
 	cfg.dst_addr = host->phy_regs + fifo_offset;
 	cfg.src_addr = cfg.dst_addr;
 	cfg.dst_addr_width = DMA_SLAVE_BUSWIDTH_4_BYTES;