patch 9.0.2175: Compile error with Motif UI + mouse support

Problem:  Compile error with Motif UI + mouse support (after v9.0.1262)
Solution: Use correct oldval option pointer

Fix compilation error introduced by 9.0.1262 and found in #13704.

closes: #13726

Signed-off-by: Ken Takata <kentkt@csc.jp>
Signed-off-by: Christian Brabandt <cb@256bit.org>

src/optionstr.c

@@ -2956,7 +2956,7 @@ did_set_mousemodel(optset_T *args UNUSED)
     if (check_opt_strings(p_mousem, p_mousem_values, FALSE) != OK)
 	return e_invalid_argument;
 #if defined(FEAT_GUI_MOTIF) && defined(FEAT_MENU) && (XmVersion <= 1002)
-    else if (*p_mousem != *oldval)
+    else if (*p_mousem != *args->os_oldval.string)
 	// Changed from "extend" to "popup" or "popup_setpos" or vv: need
 	// to create or delete the popup menus.
 	gui_motif_update_mousemodel(root_menu);

src/version.c

@@ -704,6 +704,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    2176,
 /**/
     2175,
 /**/