staging: iio: ad7192: Fix - use the dedicated reset function avoiding dma from stack.

Depends on: 691c4b95d1 ("iio: ad_sigma_delta: Implement a dedicated reset function")

SPI host drivers can use DMA to transfer data, so the buffer should be properly allocated.
Keeping it on the stack could cause an undefined behavior.

The dedicated reset function solves this issue.

Signed-off-by: Stefan Popa <stefan.popa@analog.com>
Acked-by: Lars-Peter Clausen <lars@metafoo.de>
Acked-by: Michael Hennerich <michael.hennerich@analog.com>
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>