mfd: sec-core: Fix I2C dummy device resource leak on probe failure

Dummy I2C device allocated in sec_pmic_probe() leaked if
devm_regmap_init_i2c() failed. Unregister it before returning from
probe.

Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Reviewed-by: Sachin Kamat <sachin.kamat@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>