bcma: gpio: set of_node regardless of the host type

DT allows describing many device types, not only platform ones. If e.g.
bcma is hosted on PCI(e) and it has its of_node, let's pass it to the
GPIO subsystem. This allows GPIO code to handle more hardware details
not only for bcma on a SoC.

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>