perf python: Fix NULL vs IS_ERR_OR_NULL() checking

The function trace_event__tp_format_id may return ERR_PTR(-ENOMEM).  Use
IS_ERR_OR_NULL to check tp_format.

Signed-off-by: Miaoqian Lin <linmq006@gmail.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Song Liu <song@kernel.org>
Link: http://lore.kernel.org/lkml/20211211053856.19827-1-linmq006@gmail.com


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>