stm32/factoryreset: Init vfs flags before calling pyb_flash_init_vfs.
stm32/factoryreset: Init vfs flags before calling pyb_flash_init_vfs.

The vfs flags could have any random value from stack.  This bug was
introduced back in 7723dac3371ccf081c2490b33b69492dc42818bd

adafruit/circuitpython,adafruit/circuitpython,adafruit/circuitpython,adafruit/circuitpython,adafruit/circuitpython,adafruit/circuitpython