scsi: ufs: core: sysfs: Prevent div by zero

Prevent a division by 0 when monitoring is not enabled.

Fixes: 1d8613a ("scsi: ufs: core: Introduce HBA performance monitor sysfs nodes")
Cc: stable@vger.kernel.org
Signed-off-by: Gwendal Grignou <gwendal@chromium.org>
Link: https://lore.kernel.org/r/20241120062522.917157-1-gwendal@chromium.org
Reviewed-by: Can Guo <quic_cang@quicinc.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/ufs/core/ufs-sysfs.c

@@ -670,6 +670,9 @@ static ssize_t read_req_latency_avg_show(struct device *dev,
 	struct ufs_hba *hba = dev_get_drvdata(dev);
 	struct ufs_hba_monitor *m = &hba->monitor;
 
+	if (!m->nr_req[READ])
+		return sysfs_emit(buf, "0\n");
+
 	return sysfs_emit(buf, "%llu\n", div_u64(ktime_to_us(m->lat_sum[READ]),
 						 m->nr_req[READ]));
 }
@@ -737,6 +740,9 @@ static ssize_t write_req_latency_avg_show(struct device *dev,
 	struct ufs_hba *hba = dev_get_drvdata(dev);
 	struct ufs_hba_monitor *m = &hba->monitor;
 
+	if (!m->nr_req[WRITE])
+		return sysfs_emit(buf, "0\n");
+
 	return sysfs_emit(buf, "%llu\n", div_u64(ktime_to_us(m->lat_sum[WRITE]),
 						 m->nr_req[WRITE]));
 }