bcma: gpio: Switch to use fwnode instead of of_node

GPIO library now accepts fwnode as a firmware node,
so switch the driver to use it.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20220504092525.71668-1-andriy.shevchenko@linux.intel.com