USB: ps3: don't call ps3_system_bus_driver_register on other platforms

ps3_system_bus_driver_register is PS3 platform specific function.
On other platforms, it triggers WARN_ON in kref_get.

Signed-off-by: Kou Ishizaki <kou.ishizaki@toshiba.co.jp>
Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: David Brownell <dbrownell@users.sourceforge.net>
Cc: Geoff Levand <geoffrey.levand@am.sony.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>