perf hwmon_pmu: Fix uninitialized variable warning

The line_len is only set on success. Check the return value instead.

util/hwmon_pmu.c: In function ‘perf_pmus__read_hwmon_pmus’:
util/hwmon_pmu.c:742:20: warning: ‘line_len’ may be used uninitialized [-Wmaybe-uninitialized]
742 | if (line_len > 0 && line[line_len - 1] == '\n')
| ^
util/hwmon_pmu.c:719:24: note: ‘line_len’ was declared here
719 | size_t line_len;

Fixes: 53cc0b351ec9 ("perf hwmon_pmu: Add a tool PMU exposing events from hwmon in sysfs")
Signed-off-by: Michal Suchanek <[e-mail]>
Signed-off-by: Namhyung Kim <[e-mail]>

tools/perf/util/hwmon_pmu.c

···
 			continue;
 		}
 		io__init(&io, name_fd, buf2, sizeof(buf2));
-		io__getline(&io, &line, &line_len);
-		if (line_len > 0 && line[line_len - 1] == '\n')
+		if (io__getline(&io, &line, &line_len) > 0 && line[line_len - 1] == '\n')
 			line[line_len - 1] = '\0';
 		hwmon_pmu__new(pmus, buf, class_hwmon_ent->d_name, line);
 		close(name_fd);