dmaengine: at_hdmac: Return dma_cookie_status()'s ret code when txstate is NULL

dmaengine: at_hdmac: Return dma_cookie_status()'s ret code when txstate is NULL

txstate is an optional parameter used to get a struct with auxilary
transfer status information. When not provided the call to
device_tx_status() should return the status of the dma cookie. Return the
status of dma cookie when the txstate optional parameter is not provided.

Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Acked-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Link: https://lore.kernel.org/r/20221025090306.297886-1-tudor.ambarus@microchip.com
Link: https://lore.kernel.org/r/20221025090306.297886-18-tudor.ambarus@microchip.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>