i2c / ACPI: Use 0 to indicate that device does not have interrupt assigned

This is the convention used in most parts of the kernel including DT
counterpart of I2C slave enumeration. To make things consistent do the same
for ACPI I2C slave enumeration path as well.

Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Acked-by: Wolfram Sang <wsa@the-dreams.de>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>