mfd: intel_soc_pmic_core: Remove unnecessary function

Since commit 845c8770 ("i2c / ACPI: Assign IRQ for devices that have
GpioInt automatically") I2C core assigns interrupt line to I2C slave
devices with regarding to GpioInt() resources.

There is no need to repeat this in the driver.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>