perf trace: Add missing ' = ' in the default formatting of syscall returns

We lost it recently, put it back.

Before:

  789.499 ( 0.001 ms): libvirtd/1175 lseek(fd: 22, whence: CUR) 4328

After:

  789.499 ( 0.001 ms): libvirtd/1175 lseek(fd: 22, whence: CUR) = 4328

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Fixes: 1f63139c ("perf trace beauty: Simplify syscall return formatting")
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/builtin-trace.c

@@ -1660,7 +1660,7 @@ static int trace__sys_exit(struct trace *trace, struct perf_evsel *evsel,
 		if (ret < 0)
 			goto errno_print;
 signed_print:
-		fprintf(trace->output, ") %ld", ret);
+		fprintf(trace->output, ") = %ld", ret);
 	} else if (ret < 0) {
 errno_print: {
 		char bf[STRERR_BUFSIZE];