perf intel-pt: Fix segfault in intel_pt_print_info() with uClibc

uClibc segfaulted because NULL was passed as the format to fprintf().

That happened because one of the format strings was missing and
intel_pt_print_info() didn't check that before calling fprintf().

Add the missing format string, and check format is not NULL before calling
fprintf().

Fixes: 11fa7cb86b56d361 ("perf tools: Pass Intel PT information for decoding MTC and CYC")
Signed-off-by: Adrian Hunter <[e-mail]>
Acked-by: Namhyung Kim <[e-mail]>
Cc: Adrian Hunter <[e-mail]>
Cc: Ian Rogers <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Cc: [e-mail]
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/util/intel-pt.c

···
 	[INTEL_PT_SNAPSHOT_MODE]	= "  Snapshot mode       %"PRId64"\n",
 	[INTEL_PT_PER_CPU_MMAPS]	= "  Per-cpu maps        %"PRId64"\n",
 	[INTEL_PT_MTC_BIT]		= "  MTC bit             %#"PRIx64"\n",
+	[INTEL_PT_MTC_FREQ_BITS]	= "  MTC freq bits       %#"PRIx64"\n",
 	[INTEL_PT_TSC_CTC_N]		= "  TSC:CTC numerator   %"PRIu64"\n",
 	[INTEL_PT_TSC_CTC_D]		= "  TSC:CTC denominator %"PRIu64"\n",
 	[INTEL_PT_CYC_BIT]		= "  CYC bit             %#"PRIx64"\n",
···
 	if (!dump_trace)
 		return;
 
-	for (i = start; i <= finish; i++)
-		fprintf(stdout, intel_pt_info_fmts[i], arr[i]);
+	for (i = start; i <= finish; i++) {
+		const char *fmt = intel_pt_info_fmts[i];
+
+		if (fmt)
+			fprintf(stdout, fmt, arr[i]);
+	}
 }
 
 static void intel_pt_print_info_str(const char *name, const char *str)