Documentation: Fix typo in multiple files in Documentation

Correct multiple spelling typo in Documentation.

Signed-off-by: Masanari Iida <standby24x7@gmail.com>
Acked-by: Rob Landley <rob@landley.net>
Reported-by: Anders Larsen <al@alarsen.net>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

Documentation/memory-hotplug.txt

@@ -341,7 +341,7 @@ Need more implementation yet....
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 8. Memory hotplug event notifier
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-Memory hotplug has event notifer. There are 6 types of notification.
+Memory hotplug has event notifier. There are 6 types of notification.
 
 MEMORY_GOING_ONLINE
   Generated before new memory becomes available in order to be able to