gpiolib: change gpio pin from unsigned to signed in acpi callback

The signed error will be wrongly used as valid gpio offset

Reported-by: David Binderman <dcb314@hotmail.com>
Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Qipeng Zha <qipeng.zha@intel.com>
Acked-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>