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/fs/zfs/zfs.c b/fs/zfs/zfs.c
index fb2b3ee..ca67afb 100644
--- a/fs/zfs/zfs.c
+++ b/fs/zfs/zfs.c
@@ -20,7 +20,7 @@
 #include "zfs_common.h"
 #include "div64.h"
 
-block_dev_desc_t *zfs_dev_desc;
+struct blk_desc *zfs_dev_desc;
 
 /*
  * The zfs plug-in routines for GRUB are: