CVE-2025-22094 powerpc/perf: Fix ref-counting on the PMU 'vpa_pmu'

In the Linux kernel, the following vulnerability has been resolved: powerpc/perf: Fix ref-counting on the PMU 'vpapmu' Commit 176cda0619b6 "powerpc/perf: Add perf interface to expose vpa counters" introduced 'vpapmu' to expose Book3s-HV nested APIv2 provided L1L2 context switch latency counters t...