boards: arduino_nano_33_ble: Correct polarity of pwm1 channel 0

This is a follow-up to commit f4a0ddd8.

According to the schematic, the LED connected to the P1.09 pin is
active high. Therefore, the PWM1 instance that is configured to drive
the LED should not use the "nordic,invert" property.

Signed-off-by: Andrzej Głąbek <andrzej.glabek@nordicsemi.no>