Fix typo derived from tcmalloc's pprof

The same pr is submitted into gperftools:

https://github.com/gperftools/gperftools/pull/1105

bin/jeprof.in

@@ -5367,7 +5367,7 @@ sub GetProcedureBoundaries {
   my $demangle_flag = "";
   my $cppfilt_flag = "";
   my $to_devnull = ">$dev_null 2>&1";
-  if (system(ShellEscape($nm, "--demangle", "image") . $to_devnull) == 0) {
+  if (system(ShellEscape($nm, "--demangle", $image) . $to_devnull) == 0) {
     # In this mode, we do "nm --demangle <foo>"
     $demangle_flag = "--demangle";
     $cppfilt_flag = "";