block: bdrv_aio_* do not return NULL

Initially done with the following semantic patch:

@ rule1 @
expression E;
statement S;
@@
  E =
(
   bdrv_aio_readv
|  bdrv_aio_writev
|  bdrv_aio_flush
|  bdrv_aio_discard
|  bdrv_aio_ioctl
)
     (...);
(
- if (E == NULL) { ... }
|
- if (E)
    { <... S ...> }
)

which however missed the occurrence in block/blkverify.c
(as it should have done), and left behind some unused
variables.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

hw/ide/atapi.c

@@ -352,14 +352,8 @@ static void ide_atapi_cmd_read_dma_cb(void *opaque, int ret)
     s->bus->dma->aiocb = bdrv_aio_readv(s->bs, (int64_t)s->lba << 2,
                                        &s->bus->dma->qiov, n * 4,
                                        ide_atapi_cmd_read_dma_cb, s);
-    if (!s->bus->dma->aiocb) {
-        /* Note: media not present is the most likely case */
-        ide_atapi_cmd_error(s, NOT_READY,
-                            ASC_MEDIUM_NOT_PRESENT);
-        goto eot;
-    }
-
     return;
+
 eot:
     bdrv_acct_done(s->bs, &s->acct);
     s->bus->dma->ops->add_status(s->bus->dma, BM_STATUS_INT);