scripts/spelling.txt: fix malformed entry

One of the entries has three fields "mistake||correction||correction"
rather than the expected two fields "mistake||correction".  Fix it.
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Link: https://lkml.kernel.org/r/20200930234359.255295-1-ebiggers@kernel.orgSigned-off-by: Linus Torvalds <torvalds@linux-foundation.org>

scripts/spelling.txt

@@ -589,7 +589,7 @@ explictly||explicitly
 expresion||expression
 exprimental||experimental
 extened||extended
-exteneded||extended||extended
+exteneded||extended
 extensability||extensibility
 extention||extension
 extenstion||extension