msm: perf: Fix cpu id logic in tracectr notifier

The code in tracecounter context switch notifier was using
smp_processor_id() in order to get cpu number. This was resulting
into following dmesg error: "BUG: using smp_processor_id() in
preemptible [00000000] code".
Use thread_info struct to get the cpu #.

Change-Id: Ic7c995d2c2bc25c4389248854dec91fb84ce3128
Signed-off-by: Sheetal Sahasrabudhe <sheetals@codeaurora.org>