drivers: hwinfo: stm32: fix reset flags handling for STM32C5 #6

Job	Run time
Devicetree script tests (3.13, ubuntu-24.04)	1m 1s
Devicetree script tests (3.13, windows-2025)	2m 35s
Devicetree script tests (3.12, macos-14)	57s
Devicetree script tests (3.13, macos-14)	1m 2s
Devicetree script tests (3.12, ubuntu-24.04)	59s
Devicetree script tests (3.12, windows-2025)	2m 28s
	9m 2s

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