drivers: adc: stm32 disable the ADC before setting the Oversampling
drivers: adc: stm32 disable the ADC before setting the Oversampling

On those STM32 series, setting of this feature is conditioned to
the ADC state: it is allowed to set/reset the oversampler (OVSE bit)
and set the Oversampling ratio (OVSR bits) in the ADC_CFGR2 register
only when ADC is disabled or enabled without conversion on going.
Then is the ADC re-enabled.

Signed-off-by: Francois Ramu <b83adc7f8a23ee911a37fcb61c4033581aae0b7a@st.com>

finikorg/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,finikorg/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,finikorg/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr