clk: ti: mux: convert TI mux clock to use its internal data representation

Instead of using the generic clock driver data struct, use one internal
for the TI clock driver itself. This allows modifying the register access
parts in subsequent patch.

Signed-off-by: Tero Kristo <t-kristo@ti.com>
Acked-by: Tony Lindgren <tony@atomide.com>