A significant portion of this driver lacks error handling.  As a first
step, add error paths to bcm_gpio_set_power(), bcm_open(), bcm_close(),
bcm_suspend_device(), bcm_resume_device(), bcm_resume(), bcm_probe() and
bcm_serdev_probe().  (I've also scrutinized bcm_suspend() but think it's
fine as is.)

Those are all the functions accessing the device wake and shutdown GPIO.
On Apple Macs the pins are accessed through ACPI methods, which may fail
for various reasons, hence proper error handling is necessary.  Non-Macs
access the pins directly, which may fail as well but the GPIO core does
not yet pass back errors to consumers.

Cc: Frédéric Danis <frederic.danis.oss@gmail.com>
Cc: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>