iommu/amd: Fix I/O page table memory leak

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

iommu/amd: Fix I/O page table memory leak

The current logic updates the I/O page table mode for the domain

before calling the logic to free memory used for the page table.

This results in IOMMU page table memory leak, and can be observed

when launching VM w/ pass-through devices.

Fix by freeing the memory used for page table before updating the mode.