perf/amd/uncore: Simplify code, use free_percpu()'s built-in check for NULL

free_percpu() has its own check for NULL, no need to open-code it.

Signed-off-by: Kim Phillips <kim.phillips@amd.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210817221048.88063-5-kim.phillips@amd.com