iio: adc: ad7606: move 'val' pointer to ad7606_scan_direct()

iio: adc: ad7606: move 'val' pointer to ad7606_scan_direct()

The ad7606_scan_direct() function returns 'int', which is fine for 16-bit
samples.
But when going to 18-bit samples, these need to be implemented as 32-bit
(or int) type.

In that case when getting samples (which can be negative), we'd get random
error codes.
So, the easiest thing is to just move the 'val' pointer to
'ad7606_scan_direct()'. This doesn't qualify as a fix, it's just a
preparation for 18-bit ADCs (of the AD7606 family).

Reviewed-by: David Lechner <dlechner@baylibre.com>
Signed-off-by: Alexandru Ardelean <aardelean@baylibre.com>
Link: https://patch.msgid.link/20240919130444.2100447-3-aardelean@baylibre.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>