[NUCLEO_F401RE] Remove call to Systick

+ Update Cube F4 HAL driver to V1.1.0RC2
[NUCLEO_F401RE] Correct PWM channel on PA_3
[NUCLEO_F401RE] Add missing IT flag reset + update system clock variable
Merge pull request #342 from bcostm/master

[NUCLEO_F401RE] Remove call to Systick + bug fixes