clk: imx: use imx8m_clk_hw_composite_bus for i.MX8M bus clk slice

Switch the bus clk use imx8m_clk_hw_composite_bus, then
we could avoid possible issue when setting mux of the clk.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
Reviewed-by: Dong Aisheng <aisheng.dong@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>