stm32: fix systick get_time_since_boot() bad value due to non-atomic memory read#925

Grazfather merged 2 commits intoZigEmbeddedGroup:mainZigEmbeddedGroup/microzig:mainfrom

mihainicolae80:stm32/fix-systick-get_time_since_bootmihainicolae80/microzig:stm32/fix-systick-get_time_since_bootCopy head branch name to clipboard