gpiolib: acpi: Use temporary variable for struct acpi_gpio_info

Use temporary variable to access the struct acpi_gpio_info members.
This will help further changes to be cleaner. No functional change
intended.

Acked-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>