[ARM] omap: fix build error in ohci-omap.c

drivers/usb/host/ohci-omap.c: In function 'ohci_omap_init':
drivers/usb/host/ohci-omap.c:228: error: 'start_hnp' undeclared (first use in this function)

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>