mfd: sec-core: Fix possible NULL pointer dereference when i2c_new_dummy error

During probe the sec-core driver allocates dummy I2C device for RTC with
i2c_new_dummy() but return value is not checked. In case of error
(i2c_new_device(): memory allocation failure or I2C address cannot be
used) this function returns NULL which is later used by
devm_regmap_init_i2c() or i2c_unregister_device().

If i2c_new_dummy() fails for RTC device, fail also the probe for main
MFD driver.

Cc: stable@vger.kernel.org
Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>