ftrace: Avoid crashing if format doesn't match expectations

Kernel commit 0b04d4c0542e("f2fs: Fix f2fs_truncate_partial_nodes ftrace
event") changed the format of an event in a way that causes perfetto to
hit a PERFETTO_FATAL.

The PERFETTO_FATAL was probably not intentional there, it was added
(probably by mistake) by 6db99a9ca272("Add PERFETTO_DFATAL.").

In any case, perfetto shouldn't crash for an event it doesn't
understand.

Bug: 281660544
Change-Id: I20769f4ce47a2af4c90b87e4bfb709468b4568cf
(cherry picked from commit f1ee130d2d4fa37f3c57b4f05019d664ae6523a5)