ARM: dts: stm32: Repair ethernet operation on AV96

The AV96 RGMII uses different pinmux for ETH_RGMII_TXD0, ETH_RGMII_RXD2
and ETH_RGMII_TX_CTL. Use the correct pinmux to make ethernet operational.

Reviewed-by: Patrice Chotard <patrice.chotard@st.com>
Reviewed-by: Patrick Delaunay <patrick.delaunay@st.com>
Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Cc: Patrick Delaunay <patrick.delaunay@st.com>
Cc: Patrice Chotard <patrice.chotard@st.com>