MIPS: PNX8550: use OHCI platform driver

Change the PNX8550 platform code to register an ohci-platform driver instead
of ohci-pnx8550 since the ohci-platform is suitable for use.

Signed-off-by: Florian Fainelli <florian@openwrt.org>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>