scsi-disk: Use positive return value for status in dma_readv/writev

scsi-disk: Use positive return value for status in dma_readv/writev

In some error cases, scsi_block_sgio_complete() never calls the passed
callback, but directly completes the request. This leads to bugs because
its error paths are not exact copies of what the callback would normally
do.

In preparation to fix this, allow passing positive return values to the
callbacks that represent the status code that should be used to complete
the request.

scsi_handle_rw_error() already handles positive values for its ret
parameter because scsi_block_sgio_complete() calls directly into it.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <20240731123207.27636-2-kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>