nrf/pwm: Remove superfluous NULL in machine_hard_pwm_instances.
nrf/pwm: Remove superfluous NULL in machine_hard_pwm_instances.

Remove unneeded NULL entry in machine_hard_pwm_instances[] when not
building for NRF52_SERIES.

selste/micropython,trezor/micropython,trezor/micropython,pozetroninc/micropython,kerneltask/micropython,tobbad/micropython,MrSurly/micropython,bvernoux/micropython,pozetroninc/micropython,pramasoul/micropython,trezor/micropython,kerneltask/micropython,pfalcon/micropython,MrSurly/micropython,pramasoul/micropython,bvernoux/micropython,trezor/micropython,pramasoul/micropython,bvernoux/micropython,tobbad/micropython,henriknelson/micropython,henriknelson/micropython,pfalcon/micropython,pozetroninc/micropython,kerneltask/micropython,pramasoul/micropython,selste/micropython,pfalcon/micropython,adafruit/circuitpython,adafruit/circuitpython,tobbad/micropython,selste/micropython,selste/micropython,kerneltask/micropython,henriknelson/micropython,adafruit/circuitpython,MrSurly/micropython,trezor/micropython,tobbad/micropython,pramasoul/micropython,henriknelson/micropython,kerneltask/micropython,pfalcon/micropython,pozetroninc/micropython,adafruit/circuitpython,bvernoux/micropython,MrSurly/micropython,bvernoux/micropython,henriknelson/micropython,pozetroninc/micropython,selste/micropython,pfalcon/micropython,adafruit/circuitpython,adafruit/circuitpython,MrSurly/micropython,tobbad/micropython