scripts/spelling.txt: add "issus" typo

Add "issus" and correct it as "issues".

Link: http://lkml.kernel.org/r/20200105221950.8384-1-luca@lucaceresoli.net
Signed-off-by: Luca Ceresoli <luca@lucaceresoli.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

scripts/spelling.txt

@@ -801,6 +801,7 @@ ireelevant||irrelevant
 irrelevent||irrelevant
 isnt||isn't
 isssue||issue
+issus||issues
 iternations||iterations
 itertation||iteration
 itslef||itself