nrfx: hal: nrf_comp: patch main_mode and speed_mode set

[bjarki-andreasen]

The functions for setting the main and speed modes don't clear their fields before setting the desired value. This results in not being able to set the main mode to single-ended (0) after having set the mode to differential (1), similarly, the speed mode can not be set to low (0) after being set to medium (1) or high (2), and it can be set to the reserved value 3.