usb: ehci-omap: Fix deferred probe for phy handling

PHY model is being used on omap5 platforms even if port mode is not OMAP_EHCI_PORT_MODE_PHY. So don't guess if PHY is required or not based on PHY mode.

If PHY is provided in device tree, it must be required. So, if devm_usb_get_phy_by_phandle() gives us an error code other than -ENODEV (no PHY) then error out.

This fixes USB Ethernet on omap5-uevm if PHY happens to probe after EHCI thus causing a -EPROBE_DEFER.