PCI: iproc: Use module_bcma_driver to simplify the code

module_bcma_driver() makes the code simpler by eliminating
boilerplate code.

Link: https://lore.kernel.org/r/20200918030829.3946025-1-liushixin2@huawei.com


Signed-off-by: Liu Shixin <liushixin2@huawei.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Acked-by: Ray Jui <ray.jui@broadcom.com>