perf intel-pt: Fix sync_switch INTEL_PT_SS_NOT_TRACING

sync_switch is a facility to synchronize decoding more closely with the
point in the kernel when the context actually switched.

In one case, INTEL_PT_SS_NOT_TRACING state was not correctly
transitioning to INTEL_PT_SS_TRACING state due to a missing case clause.
Add it.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: stable@vger.kernel.org
Link: http://lkml.kernel.org/r/1527762225-26024-2-git-send-email-adrian.hunter@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>