perf symbols: Fix multiple initialization of symbol system

By returning immediately if it was already initialized, do it as well at
symbol__exit, refusing multiple deinitializations.

This fixes problems in the kmem, sched and timechart commands.

Reported-by: Davidlohr Bueso <dave@gnu.org>
Cc: Davidlohr Bueso <dave@gnu.org>
Signed-off-by: Jovi Zhang <bookjovi@gmail.com>
LKML-Reference: AANLkTi=9Cn=R8SPMCRp5z+gEjXbaBHeb-AaOtRbuwwcn@mail.gmail.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
diff --git a/tools/perf/util/symbol.h b/tools/perf/util/symbol.h
index b7a8da4..ea95c27 100644
--- a/tools/perf/util/symbol.h
+++ b/tools/perf/util/symbol.h
@@ -69,7 +69,8 @@
 			show_nr_samples,
 			use_callchain,
 			exclude_other,
-			show_cpu_utilization;
+			show_cpu_utilization,
+			initialized;
 	const char	*vmlinux_name,
 			*source_prefix,
 			*field_sep;