compositor-wayland: Use the correct list pointer when freeing shm buffers

The wl_list_for_each operation on the free_buffers list should use
free_link not link, which is a different list.

This fixes a crash when entering fullscreen mode when using the pixman
renderer on the wayland back-end.

Signed-off-by: Derek Foreman <derekf@osg.samsung.com>
1 file changed