scsi: core: Use eh_timeout for START STOP UNIT

In some scenarios START STOP UNIT may time out. The default recovery
time of 30 seconds is relatively large. Modifying rq_timeout to adjust
the START STOP UNIT timeout value will affect the regular I/O.

Commit 9728c081 ("[SCSI] make scsi_eh_try_stu use block timeout")
switched to rq_timeout for the START STOP UNIT command. However commit
0816c925

 ("[SCSI] Allow error handling timeout to be specified")
introduced an explicit eh_timeout parameter. It makes more sense to
use this value as the timeout for START STOP UNIT.

Link: https://lore.kernel.org/r/1636507412-21678-1-git-send-email-brookxu.cn@gmail.com
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Wu Bo <wubo40@huawei.com>
Signed-off-by: Chunguang Xu <brookxu@tencent.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>