boards: st: nucleo_n657x0_q: correct led polarity

As is apparent on the nucleo-n657x0-q schematics[1], all of the three
user leds are controlled via. active low gpios.

Correct the polarity of the leds.

[1] https://www.st.com/resource/en/schematic_pack/mb1940-n657x0q-c02-schematic.pdf



Signed-off-by: Emil Dahl Juhl <emil@s16s.ai>