clk: mediatek: mux: Drop unused clock ops

Three out of the four defined clock ops are unused. Drop them.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Link: https://lore.kernel.org/r/20210125170819.26130-2-laurent.pinchart@ideasonboard.com


Signed-off-by: Stephen Boyd <sboyd@kernel.org>