Change KM_SLEEP to TQ_SLEEP in spa_deadman()

Since they both evaluate to zero, this is a semi-cosmetic change
but the latter is the proper value to use as an argument to
taskq_dispatch_delay().

Signed-off-by: Tim Chase <tim@chase2k.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes openzfs#4393

module/zfs/spa_misc.c

@@ -529,7 +529,7 @@ spa_deadman(void *arg)
 		vdev_deadman(spa->spa_root_vdev);
 
 	spa->spa_deadman_tqid = taskq_dispatch_delay(system_taskq,
-	    spa_deadman, spa, KM_SLEEP, ddi_get_lbolt() +
+	    spa_deadman, spa, TQ_SLEEP, ddi_get_lbolt() +
 	    NSEC_TO_TICK(spa->spa_deadman_synctime));
 }