USB: OHCI: add a name for the platform-private field

This patch adds an ohci->priv field for private use by OHCI
platform drivers.

Until now none of the platform drivers has used this private space,
but that's about to change in the next patch of this series.

Signed-off-by: Manjunath Goudar <manjunath.goudar@linaro.org>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>