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>

cmd/usb.c

@@ -625,7 +625,7 @@ static int do_usb(cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[])
 	int i;
 	extern char usb_started;
 #ifdef CONFIG_USB_STORAGE
-	block_dev_desc_t *stor_dev;
+	struct blk_desc *stor_dev;
 #endif
 
 	if (argc < 2)