block: Rename BlockDriverCompletionFunc to BlockCompletionFunc

I'll use it with block backends shortly, and the name is going to fit
badly there.  It's a block layer thing anyway, not just a block driver
thing.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
diff --git a/block/iscsi.c b/block/iscsi.c
index 3ca2951..233f462 100644
--- a/block/iscsi.c
+++ b/block/iscsi.c
@@ -665,7 +665,7 @@
 
 static BlockAIOCB *iscsi_aio_ioctl(BlockDriverState *bs,
         unsigned long int req, void *buf,
-        BlockDriverCompletionFunc *cb, void *opaque)
+        BlockCompletionFunc *cb, void *opaque)
 {
     IscsiLun *iscsilun = bs->opaque;
     struct iscsi_context *iscsi = iscsilun->iscsi;