drivers: adc: stm32h7 has a different oversampling config API

The LL_ADC_ConfigOverSamplingRatioShift function for
the stm32H7xx soc serie differs from other for the 'ratio':
"This parameter can be in the range from 1 to 1024"
Note that in the stm32h7xx_ll_adc.c the LL_ADC_OVS_RATIO_xxx value is
defined for ADC of type ADC_VER_V5_V90.

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