patch 8.1.1974: Coverity warns for using pointer as array

Problem:    Coverity warns for using pointer as array.
Solution:   Call var2fpos() directly instead of using f_line().

src/version.c

@@ -761,6 +761,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1974,
 /**/
     1973,
 /**/