Fix perf probe to use symtab only if there is no debuginfo, because debuginfo
has more information than symtab.

If we can't find a function in debuginfo, we never find it in symtab.
Signed-off-by: Masami Hiramatsu <mhiramat@redhat.com>
Reported-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
LKML-Reference: <20100421195624.24664.46214.stgit@localhost6.localdomain6>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>