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/include/usb_mass_storage.h b/include/usb_mass_storage.h
index 5804b70..8229f62 100644
--- a/include/usb_mass_storage.h
+++ b/include/usb_mass_storage.h
@@ -23,7 +23,7 @@
 	unsigned int start_sector;
 	unsigned int num_sectors;
 	const char *name;
-	block_dev_desc_t block_dev;
+	struct blk_desc block_dev;
 };
 
 int fsg_init(struct ums *ums_devs, int count);