cpufreq: amd-pstate: add check for cpufreq_cpu_get's return value

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kernel: cpufreq: amd-pstate-ut: Fix kernel panic when loading the driver

A reference leak flaw was found in the Linux kernel's AMD P-state unit test driver in the CPU policy access logic. A local user can trigger this issue by loading the amd-pstate-ut driver, which acquires CPU policy references via cpufreqcpuget without releasing them via cpufreqcpuput. This causes...