SRV_Channel: fix RCInxScaled when input is range (instead of angle) #33283

Job	Run time
build (stm32f7, chibios, 10)	6m 39s
build (stm32h7, chibios, 10)	5m 47s
build (fmuv2-plane, chibios, 10)	1m 50s
build (periph-build, chibios, 10)	4m 47s
build (iofirmware, chibios, 10)	1m 48s
build (CubeOrange-bootloader, chibios, 10)	1m 12s
build (fmuv3-bootloader, chibios, 10)	49s
build (revo-bootloader, chibios, 10)	1m 33s
build (stm32h7-debug, chibios, 10)	3m 43s
build (fmuv3, chibios, 10)	4m 56s
build (revo-mini, chibios, 10)	4m 4s
build (MatekF405-Wing, chibios, 10)	5m 48s
build (CubeOrange-ODID, chibios, 10)	3m 32s
build (CubeRedPrimary-bootloader, chibios, 10)	52s
build (configure-all, chibios, 10)	10m 28s
build (build-options-defaults-test, chibios, 10)	6m 2s
build (signing, chibios, 10)	2m 46s
	1h 6m 36s

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