phy: phy-brcm-usb-init: Fix power down USB 3.0 PHY when XHCI reenabled

Unset is required to enable USB 3.0 PHY when XHCI reenabled in response
to setting PHY3_IDDQ_OVERRIDE in uninit().

Fixes: cd6f769f ("phy: phy-brcm-usb-init: Power down USB 3.0 PHY when XHCI disabled")
Signed-off-by: Jaedon Shin <jaedon.shin@gmail.com>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>