perf parse-events: Fix NULL check against wrong variable

We did a null check after "tmp->symbol = strdup(...)", but we checked
"list->symbol" other than "tmp->symbol".

Reviewed-by: John Garry <[e-mail]>
Signed-off-by: Weiguo Li <[e-mail]>
Cc: Alexander Shishkin <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Cc: Mark Rutland <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/util/parse-events.c

···
 	for (i = 0; i < ARRAY_SIZE(symbols); i++, tmp++) {
 		tmp->type = symbols[i].type;
 		tmp->symbol = strdup(symbols[i].symbol);
-		if (!list->symbol)
+		if (!tmp->symbol)
 			goto err_free;
 	}