block: Fix error code in multiwrite for immediate failures

Signed-off-by: NKevin Wolf <kwolf@redhat.com>
Signed-off-by: NAurelien Jarno <aurelien@aurel32.net>

block.c

@@ -1881,10 +1881,10 @@ int bdrv_aio_multiwrite(BlockDriverState *bs, BlockRequest *reqs, int num_reqs)
             // submitted yet. Otherwise we'll wait for the submitted AIOs to
             // complete and report the error in the callback.
             if (mcb->num_requests == 0) {
-                reqs[i].error = EIO;
+                reqs[i].error = -EIO;
                 goto fail;
             } else {
-                mcb->error = EIO;
+                mcb->error = -EIO;
                 break;
             }
         } else {