clk: mediatek: clk-mtk: Add dummy clock ops

In order to migrate some (few) old clock drivers to the common
mtk_clk_simple_probe() function, add dummy clock ops to be able
to insert a dummy clock with ID 0 at the beginning of the list.

Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: Miles Chen <miles.chen@mediatek.com>
Reviewed-by: Chen-Yu Tsai <wenst@chromium.org>
Tested-by: Miles Chen <miles.chen@mediatek.com>
Link: https://lore.kernel.org/r/20230120092053.182923-8-angelogioacchino.delregno@collabora.com


Tested-by: Mingming Su <mingming.su@mediatek.com>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>