CVE-2026-74277: iommu/dma-iommu: Fix wrong scatterlist length assignment in P2PDMA path

In the Linux kernel, the following vulnerability has been resolved:

iommu/dma-iommu: Fix wrong scatterlist length assignment in P2PDMA path

In iommudmamapsg(), when handling PCI P2PDMA cases, the DMA length of the current scatterlist segment s is incorrectly assigned from the head entry sg->length instead of the current entry s->length.

This typo causes all P2PDMA segments in the scatterlist to inherit the length of the first segment, leading to corrupted DMA lengths for multi- segment scatterlists.

Fix this by using s->length instead of sg->length.