patch 9.0.1330: handling new value of an option has a long "else if" chain

Problem:    Handling new value of an option has a long "else if" chain.
Solution:   Use a function pointer. (Yegappan Lakshmanan, closes #12015)
diff --git a/src/spellsuggest.c b/src/spellsuggest.c
index 6b34ec8..a600557 100644
--- a/src/spellsuggest.c
+++ b/src/spellsuggest.c
@@ -480,7 +480,7 @@
 
     if (!curwin->w_p_spell)
     {
-	did_set_spelllang(curwin);
+	parse_spelllang(curwin);
 	curwin->w_p_spell = TRUE;
     }