xen: fix isxenpmu()
This is an automated ID intended to aid in discovery of potential security vulnerabilities. The actual impact and attack plausibility have not yet been proven. This ID is fixed in Linux Kernel version v5.17.2 by commit 26911a822148bef5dcfc55e7df49cb05a18737e3, it was introduced in version v4.3 by commit bf6dfb154d935725c9a2005033ca33017b9df439. For more details please see the references link.