AP_BattMonitor: Handle allocating too many analog channels #44998

Job	Run time
build (stm32f7, chibios, 10)	3m 47s
build (stm32h7, chibios, 10)	3m 17s
build (fmuv2-plane, chibios, 10)	1m 46s
build (periph-build, chibios, 10)	3m 48s
build (iofirmware, chibios, 10)	1m 35s
build (CubeOrange-bootloader, chibios, 10)	50s
build (fmuv3-bootloader, chibios, 10)	53s
build (revo-bootloader, chibios, 10)	1m 5s
build (stm32h7-debug, chibios, 10)	2m 9s
build (fmuv3, chibios, 10)	5m 34s
build (revo-mini, chibios, 10)	4m 17s
build (MatekF405-Wing, chibios, 10)	4m 59s
build (CubeOrange-ODID, chibios, 10)	2m 48s
build (CubeRedPrimary-bootloader, chibios, 10)	48s
build (configure-all, chibios, 10)	11m 2s
build (build-options-defaults-test, chibios, 10)	6m 56s
build (signing, chibios, 10)	2m 46s
build (CubeOrange-PPP, chibios, 10)	1m 59s
build (CubeRed-EKF2, chibios, 10)	2m 20s
build (SOHW, chibios, 10)	3m 20s
build (Pixhawk6X-PPPGW, chibios, 10)	1m 10s
build (new-check, chibios, 10)	4m 20s
	1h 11m 29s

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