iio: adc: ad4030: fix error pointer dereference in probe()

iio: adc: ad4030: fix error pointer dereference in probe()

The intention here was obviously to return an error if devm_regmap_init()
fails, but the return statement was accidentally left out.  This leads to
an error pointer dereference when we call:

	ret = ad4030_detect_chip_info(st);

Add the return statement.

Fixes: ec25cf6f1ee3 ("iio: adc: ad4030: add support for ad4632-16 and ad4632-24")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Reviewed-by: Nuno Sá <nuno.sa@analog.com>
Link: https://patch.msgid.link/cc67cee7-9c65-46d2-aae3-f860fc3cc461@stanley.mountain
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>