Add dummy clk which was missed during the conversion to
mtk_clk_pdev_probe() and is required for the existing DT bindings to
keep working.
Fixes: 65c10c50c9c7 ("clk: mediatek: Migrate to mtk_clk_pdev_probe() for multimedia clocks")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Daniel Golle <daniel@xxxxxxxxxxxxxx>