greybus: gpio: use bundle device for error messages

Use the bundle device directly in gpio error messages instead of the
gpio device, as they are the same pointer.  This will make future gpio
api changes much easier to handle.

Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
Reviewed-by: Johan Hovold <johan@hovoldconsulting.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>