patch 9.0.1459: typo in name of type

Problem:    Typo in name of type.
Solution:   Change funccal_T to funccall_T. (closes #12265)
diff --git a/src/structs.h b/src/structs.h
index 79c4ac6..55a859b 100644
--- a/src/structs.h
+++ b/src/structs.h
@@ -1896,7 +1896,7 @@
 				// funccal
     int		fc_copyID;	// for garbage collection
     garray_T	fc_ufuncs;	// list of ufunc_T* which keep a reference to
-				// "func"
+				// "fc_func"
 };
 
 // structure used as item in "fc_defer"