virtio_blk: Fix initialisation of dump request structure

[sarah.walker2_arm.com]

Summary

Commit c8c37141 ("virtio_blk: Use bus_dma for command/ack buffer allocations")
failed to update initialisation of the dedicated dump request structure. This
caused a panic on attempting to dump core to a virtio_blk device.

Sponsored by: Arm Ltd

[asomers]

Works for me. Thanks for the fast fix.

[andrew]

Committed in rGf54209510b1b30b1445792db7d33401f7c7a97d6 with the wrong tag