dmaengine: k3dma: remove useless ON_WARN_ONCE()

Commit 36387a2b ("k3dma: Fix
memory handling in preparation for cyclic mode") adds few
calls to ON_WARN_ONCE() to track the use of ds_run/ds_done.

After the two fixes:
- dmaengine: k3dma: fix non-cyclic mode
- dmaengine: k3dma: fix re-free of the same descriptor
the behaviour of ds_run/ds_done is properly fixed.
The remaining ON_WARN_ONCE() are never triggered and can be
removed.

Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>