usb: host: xhci-omap: invoke board_usb_cleanup in xhci_hcd_stop

xhci omap driver has board_usb_init in xhci_hcd_init but doesn't have
the corresponding cleanup function in xhci_hcd_stop.

Fix it here by invoking board_usb_cleanup() in xhci_hcd_stop().

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Acked-by: Marek Vasut <marex@denx.de>
Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Lukasz Majewski <l.majewski@samsung.com>