compositor-wayland: Set frame callback for Pixman

Fixing 89c2f637b9, also set the output's frame_cb for the Pixman
renderer, not just GL. Fixes a segfault when using compositor-wayland
with --use-pixman.

Signed-off-by: Daniel Stone <daniels@collabora.com>
Reviewed-by: Dima Ryazanov <dima@gmail.com>
1 file changed