boards/nucleo-l4xxx: hang during ADC initialization

[krzysztof-cabaj]

Description

The code from the current master branch (exact commit later) hang during initialization of ADC, for example tests/periph/adc.
I observe this behavior using nucleo-l476rg and nucleo-l496zg.

Steps to reproduce the issue

Flash mentioned boards (or maybe other from L4xxx family) using tests/periph/adc and observe console.

Expected results

The working code should prints new measurements each 100 ms:

main(): This is RIOT! (Version: 2021.07-devel-8076-gd8bd2-HEAD)

RIOT ADC peripheral driver test

This test will sample all available ADC lines once every 100ms with
a 10-bit resolution and print the sampled results to STDIO


Successfully initialized ADC_LINE(0)
Successfully initialized ADC_LINE(1)
Successfully initialized ADC_LINE(2)
Successfully initialized ADC_LINE(3)
Successfully initialized ADC_LINE(4)
Successfully initialized ADC_LINE(5)
Successfully initialized ADC_LINE(6)
ADC_LINE(0): 317
ADC_LINE(1): 296
ADC_LINE(2): 340
ADC_LINE(3): 287
ADC_LINE(4): 214
ADC_LINE(5): 228
ADC_LINE(6): 152
ADC_LINE(0): 196
ADC_LINE(1): 232
 . . .

Actual results

Using current master branch after connection program hangs, presenting after reset only this output:

main(): This is RIOT! (Version: 2021.07-devel-10796-g216435)

RIOT ADC peripheral driver test

This test will sample all available ADC lines once every 100ms with
a 10-bit resolution and print the sampled results to STDIO

Versions

This behavior was introduced by the commit 6247b2aea4b3ab20b29f7f6da903f57bb84f4ffa.
The code from the preceding commit 4b4d77a0fe6c57f64e30a5b852e0eea2c72f87d8 works.

I could fix this issue using dirty hack with defines:

#if defined(CPU_MODEL_STM32L476RG) || defined(CPU_MODEL_STM32L496ZG) 
  //old clock configuration code
#else
 //new clock configuration code
#endif

... but maybe there is a better solution.