perf util: Take elf_name as const string in dso__demangle_sym

The input string is not modified and thus can be passed in as a pointer
to const data.

Signed-off-by: Milian Wolff <milian.wolff@kdab.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Yao Jin <yao.jin@linux.intel.com>
Link: http://lkml.kernel.org/r/20170806212446.24925-3-milian.wolff@kdab.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/symbol-elf.c

@@ -391,7 +391,7 @@ out_elf_end:
 	return 0;
 }
 
-char *dso__demangle_sym(struct dso *dso, int kmodule, char *elf_name)
+char *dso__demangle_sym(struct dso *dso, int kmodule, const char *elf_name)
 {
 	return demangle_sym(dso, kmodule, elf_name);
 }