perf tools: Handle both versions of ftrace output

The ftrace output events can have either arguments or no
arguments. The parser needs to be able to handle both.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
LKML-Reference: <20091014194359.790221427@goodmis.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>