perf header: Fix memory leak for the "Not caching a kptr_restrict'ed /proc/kallsyms" case

cppcheck reported:
[util/header.c:316]: (error) Memory leak: filename
[util/header.c:316]: (error) Memory leak: linkname

Signed-off-by: Thomas Jarosch <thomas.jarosch@intra2net.com>
Link: http://lkml.kernel.org/r/9377388.0eFDp53iW6@storm
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>