trivial: fix typo in tracing documentation

Signed-off-by: Michal Sojka <sojkam1@fel.cvut.cz>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

Documentation/trace/events.txt

@@ -72,7 +72,7 @@ To enable all events in sched subsystem:
 
 	# echo 1 > /sys/kernel/debug/tracing/events/sched/enable
 
-To eanble all events:
+To enable all events:
 
 	# echo 1 > /sys/kernel/debug/tracing/events/enable