Perf: Fix PID for tracepoints
Make previous value of PID a per_cpu variable. This is required to get the correct value for previous_pid. Change-Id: I63baf8164ae9226189c745339b122d806901789d Signed-off-by: Sheetal Sahasrabudhe <sheetals@codeaurora.org>

Signed-off-by: evolutionmod <kernelcraft@gmail.com>