dmaengine: owl: Fix warnings generated during build

Following warnings are generated when compiled with W=1,

drivers/dma/owl-dma.c:170: warning: Function parameter or member 'cyclic'
not described in 'owl_dma_txd'
drivers/dma/owl-dma.c:198: warning: Function parameter or member 'cfg' not
described in 'owl_dma_vchan'
drivers/dma/owl-dma.c:198: warning: Function parameter or member 'drq' not
described in 'owl_dma_vchan'
drivers/dma/owl-dma.c:225: warning: Function parameter or member 'irq' not
described in 'owl_dma'

Fix this by adding comments for relevant struct members to appear in
kernel-doc.

Fixes: d64e1b3f5cce ("dmaengine: owl: Add Slave and Cyclic mode support for
Actions Semi Owl S900 SoC")

Reported-by: Vinod Koul <[e-mail]>
Signed-off-by: Manivannan Sadhasivam <[e-mail]>
Reviewed-by: Andreas Färber <[e-mail]>
Signed-off-by: Vinod Koul <[e-mail]>

drivers/dma/owl-dma.c

···
  * struct owl_dma_txd - Wrapper for struct dma_async_tx_descriptor
  * @vd: virtual DMA descriptor
  * @lli_list: link list of lli nodes
+ * @cyclic: flag to indicate cyclic transfers
  */
 struct owl_dma_txd {
 	struct virt_dma_desc	vd;
···
  * @vc: wrappped virtual channel
  * @pchan: the physical channel utilized by this channel
  * @txd: active transaction on this channel
+ * @cfg: slave configuration for this channel
+ * @drq: physical DMA request ID for this channel
  */
 struct owl_dma_vchan {
 	struct virt_dma_chan	vc;
···
  * @clk: clock for the DMA controller
  * @lock: a lock to use when change DMA controller global register
  * @lli_pool: a pool for the LLI descriptors
+ * @irq: interrupt ID for the DMA controller
  * @nr_pchans: the number of physical channels
  * @pchans: array of data for the physical channels
  * @nr_vchans: the number of physical channels