drivers/clock_control: stm32 fix struct wrongly dereferenced
drivers/clock_control: stm32 fix struct wrongly dereferenced

This commit fixes several occurences where a struct members is wrongly
dereferenced, which causes a compile error in case the msi clock is used
as system clock.
Only affects stm32wb and stm32wl with MSI selected as sysclock.

Signed-off-by: Thomas Stranger <289fb7da2789c69f49f06a4b4e006530cf91f1de@outlook.com>

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