Switch to use managed variant of acpi_dev_add_driver_gpios() to simplify
error path and fix potentially wrong assignment if ->probe() fails.

While here, add a debug message in case assignment fails to allow user
see the cause of a potential issue.
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Felipe Balbi <felipe.balbi@linux.intel.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>