dm io: remove struct padding

Rearrange struct dm_io.
Shrinks size from 40 -> 32 allowing more objects/slab.

Signed-off-by: Richard Kennedy <[e-mail]>
Signed-off-by: Alasdair G Kergon <[e-mail]>

drivers/md/dm.c

···
 struct dm_io {
 	struct mapped_device *md;
 	int error;
-	struct bio *bio;
 	atomic_t io_count;
+	struct bio *bio;
 	unsigned long start_time;
 };