mfd: intel_soc_pmic_bxtwc: Utilize devm_* functions in driver probe

Cleanup the resource allocation/free code in probe function by using
devm_* calls.

Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>