AP_EFI: check bounds of serial buffer in Hirth serial driver #37352

Job	Run time
build (stm32f7, chibios, 10)	3m 51s
build (stm32h7, chibios, 10)	3m 42s
build (fmuv2-plane, chibios, 10)	1m 56s
build (periph-build, chibios, 10)	3m 41s
build (iofirmware, chibios, 10)	1m 28s
build (CubeOrange-bootloader, chibios, 10)	55s
build (fmuv3-bootloader, chibios, 10)	50s
build (revo-bootloader, chibios, 10)	55s
build (stm32h7-debug, chibios, 10)	2m 16s
build (fmuv3, chibios, 10)	5m 12s
build (revo-mini, chibios, 10)	3m 54s
build (MatekF405-Wing, chibios, 10)	4m 13s
build (CubeOrange-ODID, chibios, 10)	2m 35s
build (CubeRedPrimary-bootloader, chibios, 10)	1m 12s
build (configure-all, chibios, 10)	9m 41s
build (build-options-defaults-test, chibios, 10)	7m 25s
build (signing, chibios, 10)	2m 44s
build (CubeOrange-PPP, chibios, 10)	2m 8s
build (SOHW, chibios, 10)	3m 24s
build (Pixhawk6X-PPPGW, chibios, 10)	1m 38s
	1h 3m 40s

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