scripts/spelling.txt: add "unneded" pattern and fix typo instances

Fix typos and add the following to the scripts/spelling.txt:

  unneded||unneeded

Link: http://lkml.kernel.org/r/1481573103-11329-15-git-send-email-yamada.masahiro@socionext.com
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/ocfs2/dlm/dlmmaster.c

@@ -2924,7 +2924,7 @@ again:
 	/*
 	 * if target is down, we need to clear DLM_LOCK_RES_BLOCK_DIRTY for
 	 * another try; otherwise, we are sure the MIGRATING state is there,
-	 * drop the unneded state which blocked threads trying to DIRTY
+	 * drop the unneeded state which blocked threads trying to DIRTY
 	 */
 	spin_lock(&res->spinlock);
 	BUG_ON(!(res->state & DLM_LOCK_RES_BLOCK_DIRTY));