spelling.txt: add "unnecessary" typo variants

Add unnecessary typos by copying the necessary typos.

Link: http://lkml.kernel.org/r/1505074722.22023.6.camel@perches.com
Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

scripts/spelling.txt

@@ -1187,6 +1187,10 @@ unknonw||unknown
 unknow||unknown
 unkown||unknown
 unneded||unneeded
+unneccecary||unnecessary
+unneccesary||unnecessary
+unneccessary||unnecessary
+unnecesary||unnecessary
 unneedingly||unnecessarily
 unnsupported||unsupported
 unmached||unmatched