iommu/dma: add missing support for DMA_ATTR_MMIO for dma_iova_unlink()

iommu/dma: add missing support for DMA_ATTR_MMIO for dma_iova_unlink()

Commit c288d657dd51 added support for DMA_ATTR_MMIO attribute in the
dma_iova_link() code path, but missed that the CPU cache is being also
touched in the dma_iova_unlink() path. Fix this.

Fixes: c288d657dd51 ("iommu/dma: implement DMA_ATTR_MMIO for dma_iova_link().")
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Leon Romanovsky <leon@kernel.org>
Link: https://lore.kernel.org/r/20251124170955.3884351-1-m.szyprowski@samsung.com