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>

include/sandboxblockdev.h

@@ -8,7 +8,7 @@
 #define __SANDBOX_BLOCK_DEV__
 
 struct host_block_dev {
-	block_dev_desc_t blk_dev;
+	struct blk_desc blk_dev;
 	char *filename;
 	int fd;
 };