tools/power/x86/intel-speed-select: Process mailbox read error for core-power

Some older kernels don't support reading core-power status. In that case
mailbox command fails. So, display core-power status as "unknown" instead
of supported.
Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>

tools/power/x86/intel-speed-select/isst-config.c

@@ -959,6 +959,10 @@ static void isst_print_extended_platform_info(void)
 		fprintf(outf, "Intel(R) SST-BF (feature base-freq) is not supported\n");
 
 	ret = isst_read_pm_config(i, &cp_state, &cp_cap);
+	if (ret) {
+		fprintf(outf, "Intel(R) SST-CP (feature core-power) status is unknown\n");
+		return;
+	}
 	if (cp_cap)
 		fprintf(outf, "Intel(R) SST-CP (feature core-power) is supported\n");
 	else