ARM: dts: stm32: Rename LEDs to match silkscreen on AV96

The LED labels do not match the silkscreen on the board, fix it.

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>
Cc: Tom Rini <trini@konsulko.com>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>