iio: ti_am335x_adc: Adjust the closing bracket in tiadc_read_raw()

It somehow looks like the ending bracket belongs to the if statement but
it does belong to the while loop. This patch moves the bracket where it
belongs.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Acked-by: Jonathan Cameron <jic23@kernel.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>