iio: frequency: adf4350: add missing clk_disable_unprepare() on error in adf4350_probe()

Add the missing clk_disable_unprepare() before return
from adf4350_probe() in the error handling case.

Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Reviewed-by: Lars-Peter CLausen <lars@metafoo.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>