OHCI: Fix problem if SM501 and another platform driver is selected

If the SM501 and another platform driver, such as the SM501
then we end up defining PLATFORM_DRIVER twice. This patch
seperated the SM501 onto a seperate define of SM501_OHCI_DRIVER
so that it can be selected without overwriting the original
definition.

Signed-off-by: Ben Dooks <ben-linux@fluff.org>
Acked-by: David Brownell <dbrownell@users.sourceforge.net>
Cc: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>