AP_CANManager: use a switch statement to tidy driver allocation #40529

Job	Run time
build (stm32f7, chibios, 10)	5m 53s
build (stm32h7, chibios, 10)	5m 43s
build (fmuv2-plane, chibios, 10)	3m 57s
build (periph-build, chibios, 10)	5m 49s
build (iofirmware, chibios, 10)	3m 40s
build (CubeOrange-bootloader, chibios, 10)	2m 57s
build (fmuv3-bootloader, chibios, 10)	3m 16s
build (revo-bootloader, chibios, 10)	3m 6s
build (stm32h7-debug, chibios, 10)	4m 18s
build (fmuv3, chibios, 10)	7m 37s
build (revo-mini, chibios, 10)	6m 12s
build (MatekF405-Wing, chibios, 10)	6m 52s
build (CubeOrange-ODID, chibios, 10)	4m 41s
build (CubeRedPrimary-bootloader, chibios, 10)	3m 4s
build (configure-all, chibios, 10)	12m 21s
build (build-options-defaults-test, chibios, 10)	9m 17s
build (signing, chibios, 10)	4m 42s
build (CubeOrange-PPP, chibios, 10)	4m 10s
build (SOHW, chibios, 10)	11m 3s
build (Pixhawk6X-PPPGW, chibios, 10)	3m 23s
build (new-check, chibios, 10)	6m 15s
	1h 58m 16s

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