dm: Drop the block_dev_desc_t typedef

Use 'struct' instead of a typdef. Also since 'struct block_dev_desc' is long
and causes 80-column violations, rename it to struct blk_desc.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Tested-by: Stephen Warren <swarren@nvidia.com>
diff --git a/drivers/dfu/dfu_mmc.c b/drivers/dfu/dfu_mmc.c
index 395d472..bfac91a 100644
--- a/drivers/dfu/dfu_mmc.c
+++ b/drivers/dfu/dfu_mmc.c
@@ -351,7 +351,7 @@
 
 	} else if (!strcmp(entity_type, "part")) {
 		disk_partition_t partinfo;
-		block_dev_desc_t *blk_dev = &mmc->block_dev;
+		struct blk_desc *blk_dev = &mmc->block_dev;
 		int mmcdev = second_arg;
 		int mmcpart = third_arg;