stm32/system_stm32: Provide default value for HSI calibration.
stm32/system_stm32: Provide default value for HSI calibration.

If HSI is used the calibration value must be valid.  Fixes #4596.

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