AP_DDS: fixed cell voltages #38058

Job	Run time
build (base)	4m 35s
build (clang)	4m 32s
build-gcc-heli	6m 32s
autotest (sitltest-copter-tests1a)	7m 25s
autotest (sitltest-copter-tests1b)	9m 37s
autotest (sitltest-copter-tests1c)	11m 29s
autotest (sitltest-copter-tests1d)	8m 6s
autotest (sitltest-copter-tests1e)	8m 59s
autotest (sitltest-copter-tests2a)	9m 5s
autotest (sitltest-copter-tests2b)	28m 22s
autotest-heli (sitltest-heli)	10m 8s
	1h 48m 50s

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