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/1663666339-17560-1-git-send-email-wubo40@huawei.com


Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Wu Bo <wubo40@huawei.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>