mfd: intel_soc_pmic: Move PMIC interrupt comment to probe function

intel_soc_pmic_find_gpio_irq() tries to find a GPIO interrupt but doesn't
select between it or I2C interrupt so it makes more sense to move this
comment to intel_soc_pmic_i2c_probe() with minor edits.

Signed-off-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>