perf script: Rename struct event to struct event_format in perl engine

perf script: Rename struct event to struct event_format in perl engine

While migrating to the libtraceevent, the perl scripting engine
missed this structure rename.

This fixes:

     util/scripting-engines/trace-event-perl.c: In function "find_cache_event":
     util/scripting-engines/trace-event-perl.c:244: error: assignment from incompatible pointer type
     util/scripting-engines/trace-event-perl.c:248: error: dereferencing pointer to incomplete type
     util/scripting-engines/trace-event-perl.c:248: error: dereferencing pointer to incomplete type
     util/scripting-engines/trace-event-perl.c:250: error: dereferencing pointer to incomplete type
     util/scripting-engines/trace-event-perl.c: In function "perl_process_tracepoint":
     util/scripting-engines/trace-event-perl.c:286: error: dereferencing pointer to incomplete type
     util/scripting-engines/trace-event-perl.c:286: error: dereferencing pointer to incomplete type
     util/scripting-engines/trace-event-perl.c:307: error: dereferencing pointer to incomplete type
     util/scripting-engines/trace-event-perl.c: In function "perl_generate_script":
     util/scripting-engines/trace-event-perl.c:498: error: passing argument 1 of "trace_find_next_event" from incompatible pointer type
     util/scripting-engines/../trace-event.h:56: note: expected "struct event_format *" but argument is of type "struct event *"
     util/scripting-engines/trace-event-perl.c:498: error: assignment from incompatible pointer type
     util/scripting-engines/trace-event-perl.c:499: error: dereferencing pointer to incomplete type
     util/scripting-engines/trace-event-perl.c:499: error: dereferencing pointer to incomplete type
     util/scripting-engines/trace-event-perl.c:513: error: dereferencing pointer to incomplete type
     util/scripting-engines/trace-event-perl.c:532: error: dereferencing pointer to incomplete type
     util/scripting-engines/trace-event-perl.c:556: error: dereferencing pointer to incomplete type
     util/scripting-engines/trace-event-perl.c:569: error: dereferencing pointer to incomplete type
     util/scripting-engines/trace-event-perl.c:570: error: dereferencing pointer to incomplete type
     util/scripting-engines/trace-event-perl.c:579: error: dereferencing pointer to incomplete type
     util/scripting-engines/trace-event-perl.c:580: error: dereferencing pointer to incomplete type

Reported-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Frederic Weisbecker <fweisbec@redhat.com>
Cc: Frederic Weisbecker <fweisbec@redhat.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Namhyung Kim <namhyung.kim@lge.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Tom Zanussi <tzanussi@gmail.com>
Link: http://lkml.kernel.org/r/1337697049-30251-2-git-send-email-fweisbec@gmail.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>