Found by coccinelle / coccicheck

CHECK   drivers/iio/adc/bcm_iproc_adc.c
drivers/iio/adc/bcm_iproc_adc.c:311:3-4: Unneeded semicolon

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
Cc: Raveendra Padasalagi <raveendra.padasalagi@broadcom.com>