usb: core: Try generic PHY_MODE_USB_HOST if usb_phy_roothub_set_mode fails

Some PHYs do not support PHY_MODE_USB_HOST_SS, i.e. USB 3.0 or higher.
Fall back and try the more generic PHY_MODE_USB_HOST if it fails.

Fixes: b97a3134 ("usb: core: comply to PHY framework")
Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Tested-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>