scsi: core: Add I/O timeout count for SCSI device

Currently struct scsi_device maintains counters for requests, completions,
and errors but is missing a counter for timeouts.

For better tracking of timeouts, add a suitable counter.

Link: https://lore.kernel.org/r/[e-mail]
Reviewed-by: Bart Van Assche <[e-mail]>
Signed-off-by: Wu Bo <[e-mail]>
Signed-off-by: Martin K. Petersen <[e-mail]>

drivers/scsi/scsi_error.c

···
 	trace_scsi_dispatch_cmd_timeout(scmd);
 	scsi_log_completion(scmd, TIMEOUT_ERROR);
 
+	atomic_inc(&scmd->device->iotmo_cnt);
 	if (host->eh_deadline != -1 && !host->last_reset)
 		host->last_reset = jiffies;
 

drivers/scsi/scsi_sysfs.c

···
 show_sdev_iostat(iorequest_cnt);
 show_sdev_iostat(iodone_cnt);
 show_sdev_iostat(ioerr_cnt);
+show_sdev_iostat(iotmo_cnt);
 
 static ssize_t
 sdev_show_modalias(struct device *dev, struct device_attribute *attr, char *buf)
···
 	&dev_attr_iorequest_cnt.attr,
 	&dev_attr_iodone_cnt.attr,
 	&dev_attr_ioerr_cnt.attr,
+	&dev_attr_iotmo_cnt.attr,
 	&dev_attr_modalias.attr,
 	&dev_attr_queue_depth.attr,
 	&dev_attr_queue_type.attr,

include/scsi/scsi_device.h

···
 	atomic_t iorequest_cnt;
 	atomic_t iodone_cnt;
 	atomic_t ioerr_cnt;
+	atomic_t iotmo_cnt;
 
 	struct device		sdev_gendev,
 				sdev_dev;