usb: cdns3: fix warning when USB_CDNS_HOST is not set

Fix a build warning when USB_CDNS_HOST is not enabled:

In file included from ../drivers/usb/cdns3/core.c:23:0:
../drivers/usb/cdns3/host-export.h:27:51: warning: ‘struct usb_hcd’ declared inside parameter list will not be visible outside of this definition or declaration
 static inline int xhci_cdns3_suspend_quirk(struct usb_hcd *hcd)
                                                   ^~~~~~~

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Peter Chen <peter.chen@nxp.com>
Cc: Pawel Laszczak <pawell@cadence.com>
Cc: Roger Quadros <rogerq@ti.com>
Cc: linux-usb@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Peter Chen <peter.chen@nxp.com>