iio: adc: ad7780: Fix a resource handling path in 'ad7780_probe()'

[ Upstream commit b0536f9826a5ed3328d527b4fc1686867a9f3041 ]

If 'ad7780_init_gpios()' fails, we must not release some resources that
have not been allocated yet. Return directly instead.

Fixes: 5bb30e7d ("staging: iio: ad7780: move regulator to after GPIO init")
Fixes: 9085daa4 ("staging: iio: ad7780: add gain & filter gpio support")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Acked-by: Renato Lui Geh <renatogeh@gmail.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>