bcma: convert bus code to use dev_groups

The dev_attrs field of struct bus_type is going away soon, dev_groups
should be used instead.  This converts the bcma bus code to use the
correct field.

Acked-by: Rafał Miłecki <zajec5@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>