iio: adc: exynos: Drop a stray semicolon

Identified by coccinelle
drivers/iio/adc/exynos_adc.c:654:2-3: Unneeded semicolon

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Chanwoo Choi <cw00.choi@samsung.com>