clk: clk_stm32f: Remove STMMAC clock setup

Thanks to 'commit ba1f9667 ("net: designware: add clock support")'
we don't need anymore to setup the STMMAC clock in board.

Signed-off-by: Patrice Chotard <patrice.chotard@st.com>
Reviewed-by: Vikas Manocha <vikas.manocha@st.com>