CVE-2026-80551: s390/vfio_ccw: Ensure first IDAW remains constant

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

s390/vfioccw: Ensure first IDAW remains constant

The first IDAW in a list does not need to be on a 2K/4K boundary like all others, and so is read separately to accurately calculate the size of the buffer needed to read the full IDAL.

Verify that the address found in the first IDAW is unchanged between reads, to ensure a consistent set of IDAWs being worked with.