dmaengine: rcar-dmac: unmap slave resource when channel is freed

dmaengine: rcar-dmac: unmap slave resource when channel is freed

commit 3139dc8ded6f27552a248d23fe9f086e3027fa12 upstream.

The slave mapping should be removed together with other channel
resources when the channel is freed. If it's not unmapped it will hang
around forever after the channel is freed.

Fixes: 9f878603dbdb7db3 ("dmaengine: rcar-dmac: add iommu support for slave transfers")
Reported-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>