boards: st: nucleo_l152re: fix LED polarity in device tree

Fix incorrectly defined LED polarity (GPIO_ACTIVE_LOW → GPIO_ACTIVE_HIGH)
to match hardware schematic and ensure consistent GPIO API behavior.

Fixes: #87424
Link: https://www.st.com/en/evaluation-tools/nucleo-l152re.html#cad-resources



Signed-off-by: Roudy Dagher <roudy.dagher@gmail.com>