Fix method of accessing character string to fix Qurt compiler warning #43970

Job	Run time
build (stm32f7, chibios, 10)	3m 56s
build (stm32h7, chibios, 10)	3m 16s
build (fmuv2-plane, chibios, 10)	2m 17s
build (periph-build, chibios, 10)	4m 20s
build (iofirmware, chibios, 10)	1m 22s
build (CubeOrange-bootloader, chibios, 10)	1m 18s
build (fmuv3-bootloader, chibios, 10)	1m 12s
build (revo-bootloader, chibios, 10)	55s
build (stm32h7-debug, chibios, 10)	2m 40s
build (fmuv3, chibios, 10)	5m 40s
build (revo-mini, chibios, 10)	4m 25s
build (MatekF405-Wing, chibios, 10)	4m 45s
build (CubeOrange-ODID, chibios, 10)	2m 34s
build (CubeRedPrimary-bootloader, chibios, 10)	54s
build (configure-all, chibios, 10)	10m 41s
build (build-options-defaults-test, chibios, 10)	6m 50s
build (signing, chibios, 10)	3m 10s
build (CubeOrange-PPP, chibios, 10)	2m 19s
build (CubeRed-EKF2, chibios, 10)	2m 30s
build (SOHW, chibios, 10)	3m 25s
build (Pixhawk6X-PPPGW, chibios, 10)	1m 28s
build (new-check, chibios, 10)	4m 19s
	1h 14m 16s

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