i2c: acpi: Factor out getting the IRQ from ACPI

In preparation for future refactoring factor out the fetch of the IRQ
into its own helper function. Whilst we are at it update the handling
to return the actual error code returned from acpi_dev_get_resources
as well.

Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>