AP_Periph: fixed FSO fans #1215

Job	Run time
build (stm32f7, chibios, 10)	4m 7s
build (stm32h7, chibios, 10)	3m 49s
build (fmuv2-plane, chibios, 10)	1m 54s
build (periph-build, chibios, 10)	6m 9s
build (iofirmware, chibios, 10)	1m 21s
build (CubeOrange-bootloader, chibios, 10)	49s
build (fmuv3-bootloader, chibios, 10)	1m 8s
build (revo-bootloader, chibios, 10)	1m 12s
build (stm32h7-debug, chibios, 10)	2m 33s
build (fmuv3, chibios, 10)	5m 4s
build (revo-mini, chibios, 10)	4m 23s
build (MatekF405-Wing, chibios, 10)	4m 18s
build (CubeOrange-ODID, chibios, 10)	2m 39s
build (CubeRedPrimary-bootloader, chibios, 10)	1m 10s
build (configure-all, chibios, 10)	10m 1s
build (build-options-defaults-test, chibios, 10)	5m 49s
build (signing, chibios, 10)	3m 3s
build (CubeOrange-PPP, chibios, 10)	2m 5s
build (CubeOrange-SOHW, chibios, 10)	2m 17s
build (Pixhawk6X-PPPGW, chibios, 10)	1m 21s
	1h 5m 12s

Provide feedback