samples: tracing: run openocd sample with 1 cpu

openocd thread awareness support does not work with multiple CPUs
enabled.

Signed-off-by: Anas Nashif <anas.nashif@intel.com>
diff --git a/samples/subsys/tracing/sample.yaml b/samples/subsys/tracing/sample.yaml
index da876a4..2487e27 100644
--- a/samples/subsys/tracing/sample.yaml
+++ b/samples/subsys/tracing/sample.yaml
@@ -20,6 +20,7 @@
       - CONFIG_TRACING_CPU_STATS=y
   tracing.backends.openocd:
     extra_configs:
+      - CONFIG_MP_NUM_CPUS=1
       - CONFIG_OPENOCD_SUPPORT=y
       - CONFIG_SMP=n
     arch_exclude: posix xtensa