bindings: phy: stm32u5-otghs-phy: remove U suffix in DT snippets

After PR 79683, DTSI files were full of U-suffixed constants in the
clock configurations. This was copied verbatim in this file even
though the U prefix should not be used.

Remove the useless U suffixes in DT snippets of this binding.

Signed-off-by: Mathieu Choplain <mathieu.choplain@st.com>