perf: Use unique names for per_cpu objects

When CONFIG_DEBUG_FORCE_WEAK_PER_CPU is enabled it forces each per_cpu
object to use a unique name even if they are declared as static.
Commit 3d3eb5fb ("perf: add hotplug support") added two per_cpu
objects of the same name so arbitrarily pick one and rename it.

Fixes: 3d3eb5fb ("perf: add hotplug support")
Change-Id: Ic0dedbad44a18f63ba0051956668de9c7f3c54b8
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>