iio: adc: cpcap: Fix fall-through warnings for Clang

In preparation to enable -Wimplicit-fallthrough for Clang, fix a warning
by explicitly adding a break statement instead of letting the code fall
through to the next case.

Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Link: https://github.com/KSPP/linux/issues/115
Link: https://lore.kernel.org/r/b3c1c3f9c76f2f0e832f956587f227e44af57d3d.1605896060.git.gustavoars@kernel.org
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/adc/cpcap-adc.c

@@ -557,6 +557,7 @@ static void cpcap_adc_setup_bank(struct cpcap_adc *ddata,
 		break;
 	case CPCAP_ADC_BATTP_PI16 ... CPCAP_ADC_BATTI_PI17:
 		value1 |= CPCAP_BIT_RAND1;
+		break;
 	default:
 		break;
 	}