tracing/filters: Don't use pred on alloc failure

Dan Carpenter sent me a fix to prevent pred from being used if
it couldn't be allocated.  This updates his patch for the same
problem in the tracing tree (which has changed this code quite
substantially).

Reported-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: Tom Zanussi <tzanussi@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Li Zefan <lizf@cn.fujitsu.com>
LKML-Reference: <1249746576.6453.30.camel@tropicana>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
The original report:

create_logical_pred() could sometimes return NULL.

It's a static checker complaining rather than problems at runtime...