SDL_waylanddatamanager.c (mime_data_list_add): constify the buffer param

Fixes -Wdiscarded-qualifiers warnings from Wayland_data_source_add_data()
diff --git a/Xcode/SDL/SDL.xcodeproj/project.pbxproj b/Xcode/SDL/SDL.xcodeproj/project.pbxproj
old mode 100755
new mode 100644
diff --git a/src/video/wayland/SDL_waylanddatamanager.c b/src/video/wayland/SDL_waylanddatamanager.c
index 2a4c9c5..c72c19a 100644
--- a/src/video/wayland/SDL_waylanddatamanager.c
+++ b/src/video/wayland/SDL_waylanddatamanager.c
@@ -181,7 +181,7 @@
 static int
 mime_data_list_add(struct wl_list* list, 
                    const char* mime_type,
-                   void* buffer, size_t length)
+                   const void* buffer, size_t length)
 {
     int status = 0;
     size_t mime_type_length = 0;