mfd: intel_soc_pmic_bxtwc: Use dev_err_probe()

Simplify the mux error path a bit by using dev_err_probe().

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20220628221747.33956-4-andriy.shevchenko@linux.intel.com