perf trace: Fix IS_ERR() vs NULL check bug

The alloc_syscall_stats() function always returns an error pointer
(ERR_PTR) on failure.

So replace NULL check with IS_ERR() check after calling
alloc_syscall_stats() function.

Fixes: fc00897 ("perf trace: Add --summary-mode option")
Reviewed-by: Ian Rogers <irogers@google.com>
Signed-off-by: Fushuai Wang <wangfushuai@baidu.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

Author: Fushuai Wang

tools/perf/builtin-trace.c

@@ -4441,7 +4441,7 @@ static int trace__run(struct trace *trace, int argc, const char **argv)
 
 	if (trace->summary_mode == SUMMARY__BY_TOTAL && !trace->summary_bpf) {
 		trace->syscall_stats = alloc_syscall_stats();
-		if (trace->syscall_stats == NULL)
+		if (IS_ERR(trace->syscall_stats))
 			goto out_delete_evlist;
 	}
 
@@ -4749,7 +4749,7 @@ static int trace__replay(struct trace *trace)
 
 	if (trace->summary_mode == SUMMARY__BY_TOTAL) {
 		trace->syscall_stats = alloc_syscall_stats();
-		if (trace->syscall_stats == NULL)
+		if (IS_ERR(trace->syscall_stats))
 			goto out;
 	}