dma: ti: k3-udma: Use ring_idx to pair k3 nav rings

Use ring_idx to pair rings. ring_idx will be same as tx flow_id for all
non-negative flow_ids. For negative flow_ids, ring_idx will be tchan->id
added with bchan_cnt.

Link: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/dma/ti/k3-udma.c?h=v6.8-rc2#n1686


Signed-off-by: MD Danish Anwar <danishanwar@ti.com>
Reviewed-by: Ravi Gunasekaran <r-gunasekaran@ti.com>