virtio_blk: temporary variable type tweak

virtblk_result returns blk_status_t which is a bitwise restricted type,
so we are not supposed to stuff it in a plain int temporary variable.
All we do with it is pass it on to a function expecting blk_status_t so
the generated code is ok, but we get warnings from sparse:

drivers/block/virtio_blk.c:326:36: sparse: sparse: incorrect type in initializer (different base types) @@     expected int status @@
+got restricted blk_status_t @@
drivers/block/virtio_blk.c:334:33: sparse: sparse: incorrect type in argument 2 (different base types) @@     expected restricted
+blk_status_t [usertype] error @@     got int status @@

Make sparse happy by using the correct type.

Message-Id: <20221220124152.523531-1-mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>