AP_Periph: Change division to multiplication #701

Job	Run time
build (stm32f7, chibios, 10)	14m 45s
build (stm32h7, chibios, 10)	13m 55s
build (fmuv2-plane, chibios, 10)	7m 18s
build (periph-build, chibios, 10)	13m 45s
build (iofirmware, chibios, 10)	4m 21s
build (CubeOrange-bootloader, chibios, 10)	3m 18s
build (fmuv3-bootloader, chibios, 10)	3m 11s
build (revo-bootloader, chibios, 10)	3m 28s
build (stm32h7-debug, chibios, 10)	8m 46s
build (fmuv3, chibios, 10)	14m 56s
build (revo-mini, chibios, 10)	11m 52s
build (MatekF405-Wing, chibios, 10)	12m 47s
build (CubeOrange-ODID, chibios, 10)	9m 44s
build (CubeRedPrimary-bootloader, chibios, 10)	3m 13s
build (configure-all, chibios, 10)	12m 56s
build (build-options-defaults-test, chibios, 10)	24m 2s
build (signing, chibios, 10)	10m 42s
build (CubeOrange-PPP, chibios, 10)	8m 25s
build (CubeRed-EKF2, chibios, 10)	8m 36s
build (SOHW, chibios, 10)	13m 51s
build (Pixhawk6X-PPPGW, chibios, 10)	5m 5s
build (new-check, chibios, 10)	14m 54s
	3h 43m 50s

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