dmaengine: xilinx_dma: Correctly handle cyclic descriptor callbacks

DMA clients can provide one of two types of callbacks. For this reason
dmaengine drivers should not directly invoke `callback`, but always use
`dmaengine_desc_callback_invoke()`. This makes sure that both types of
callbacks are handled correctly.

The xilinx_dma driver currently doesn't do this for cyclic descriptors and
only handles the `callback` type callback. If the client used the
`callback_result` type callback it will not be called.

Fix this by switching to `dmaengine_desc_callback_valid()` and
`dmaengine_desc_callback_invoke()`.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Link: https://lore.kernel.org/r/20211025075428.2094-2-lars@metafoo.de
Signed-off-by: Vinod Koul <vkoul@kernel.org>