clk: imx: imx8: Fix an error handling path if devm_clk_hw_register_mux_parent_data_table() fails

If a devm_clk_hw_register_mux_parent_data_table() call fails, it is likely
that the probe should fail with an error code.

Set 'ret' before leaving the function.

Fixes: d3a0946d ("clk: imx: imx8: add audio clock mux driver")
Reviewed-by: Peng Fan <peng.fan@nxp.com>
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Abel Vesa <abel.vesa@linaro.org>