iommufd: Make sure to zero vfio_iommu_type1_info before copying to user

In the Linux kernel, the following vulnerability has been resolved: iommufd: Make sure to zero vfio_iommu_type1_info before copying to user Missed a zero initialization here. Most of the struct is filled with a copy_from_user(), however minsz for that copy is smaller than the actual struct by 8 bytes, thus we don't fill the padding.