hw/dma: sifive_pdma: Set done bit upon completion

Ensure that the 'done' bit is set upon transfer completion, even if an error occurs, since all transfers are considered completed regardless of success or failure. Signed-off-by: Jay Chang <jay.chang@sifive.com> Reviewed-by: Frank Chang <frank.chang@sifive.com> Reviewed-by: Alistair Francis <alistair.francis@wdc.com> Message-ID: <20260304030816.33209-1-jay.chang@sifive.com> Signed-off-by: Alistair Francis <alistair.francis@wdc.com>