clk: clk-mux: Fold clk_register_mux()

clk: clk-mux: Fold clk_register_mux()

Neither clk_register_mux_table() nor clk_hw_register_mux_table()
are called outside of clk-mux.c , fold both into clk_register_mux().
No functional change.

Signed-off-by: Marek Vasut <marex@denx.de>