Include: blkdev: Removed duplicate 'struct request;' declaration.

In include/linux/blkdev.h duplicate declarations of the request
struct exist.  Cleaned up by removing the second, unneeded
declaration.
Signed-off-by: NJohn Pittman <jpittman@redhat.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

include/linux/blkdev.h

@@ -47,7 +47,6 @@ struct pr_ops;
  */
 #define BLKCG_MAX_POLS		2
 
-struct request;
 typedef void (rq_end_io_fn)(struct request *, int);
 
 #define BLK_RL_SYNCFULL		(1U << 0)