brcm63xx: prevent usb clock state inconsistency on BCM6318

brcm63xx: prevent usb clock state inconsistency on BCM6318

Return the same clock for usbh and usbd on BCM6318 to prevent the clock
getting disabled despite being supposed to be enabled, e.g. by the
following sequence:

	clk_enable(usbh); <- usbh->usage = 1, enabled
	clk_enable(usbd); <- usbd->usage = 1, enabled (no effect)
	clk_disable(usbd); <- usbd->usage = 0,  -> disabled!

Signed-off-by: Jonas Gorski <jogo@openwrt.org>
git-svn-id: svn://svn.openwrt.org/openwrt/trunk@39321 3c298f89-4303-0410-b956-a3cf2f4a3e73