xen: fix is_xen_pmu()
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 v5.10.110 by commit e9445a7a59d84ed3ae6c85f299d2a6c4930b1ee9, it was introduced in version v4.3 by commit bf6dfb154d935725c9a2005033ca33017b9df439. For more details please see the references link.