stm32/mboot: Fix bug with invalid memory access of USB state.
stm32/mboot: Fix bug with invalid memory access of USB state.

Only one of pcd_fs_handle/pcd_hs_handle is ever initialised, so if both of
these USB peripherals are enabled then one of these if-statements will
access invalid memory pointed to by an uninitialised Instance.  This patch
fixes this bug by explicitly referencing the peripheral struct.

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