gpiolib: acpi: Check for errors first in acpi_find_gpio()

It's better to parse the code when the usual pattern is being used,
i.e. checking for error condition first.

There is no functional or code generation change (tested in LLVM).

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