block: implement and use [__]blk_end_request_all()

There are many [__]blk_end_request() call sites which call it with
full request length and expect full completion.  Many of them ensure
that the request actually completes by doing BUG_ON() the return
value, which is awkward and error-prone.

This patch adds [__]blk_end_request_all() which takes @rq and @error
and fully completes the request.  BUG_ON() is added to to ensure that
this actually happens.

Most conversions are simple but there are a few noteworthy ones.

* cdrom/viocd: viocd_end_request() replaced with direct calls to
  __blk_end_request_all().

* s390/block/dasd: dasd_end_request() replaced with direct calls to
  __blk_end_request_all().

* s390/char/tape_block: tapeblock_end_request() replaced with direct
  calls to blk_end_request_all().

[ Impact: cleanup ]

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Russell King <rmk@arm.linux.org.uk>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Mike Miller <mike.miller@hp.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Jeff Garzik <jgarzik@pobox.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Jeremy Fitzhardinge <jeremy@xensource.com>
Cc: Alex Dubov <oakad@yahoo.com>
Cc: James Bottomley <James.Bottomley@HansenPartnership.com>
diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index 5d34764..50745e6 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -62,7 +62,7 @@
 			break;
 		}
 
-		__blk_end_request(vbr->req, error, blk_rq_bytes(vbr->req));
+		__blk_end_request_all(vbr->req, error);
 		list_del(&vbr->list);
 		mempool_free(vbr, vblk->pool);
 	}