clk: rockchip: add CLK_IGNORE_UNUSED flag to fix rk3066/rk3188 USB Host

This patch adds CLK_IGNORE_UNUSED flag to hclk_usb_peri, hclk_usbotg0
and hclk_usbotg1 because these clocks must remain enabled to use the
USB controllers in host mode.

This fixes a regression introduced by commit 78eaf6095cc7
("clk: rockchip: disable unused clocks").

Signed-off-by: Julien CHAUVEAU <julien.chauveau@neo-technologies.fr>
Fixes: 78eaf6095cc7 ("clk: rockchip: disable unused clocks")
Reviewed-by: Romain Perier <romain.perier@gmail.com>
Tested-by: Romain Perier <romain.perier@gmail.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>