usb: dwc3: dwc3-st: Update the incorrect DT dwc3 example.

There is a subtle typo phys-names should be phy-names. Using the
current example means you don't have working usb (as you fail to
obtain the phys). Also update the example to use the generic phy
type constants which are now used for miphy28.

Additionally also remove the unnecessary new line in the example.

Signed-off-by: Peter Griffin <peter.griffin@linaro.org>
Acked-by: Rob Herring <robh@kernel.org>
Acked-by: Maxime Coquelin <maxime.coquelin@st.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>