iio: adc: ad9292: Use new structure for SPI transfer delays

In a recent change to the SPI subsystem [1], a new `delay` struct was added
to replace the `delay_usecs`. This change replaces the current
`delay_usecs` with `delay` for this driver.

The `spi_transfer_delay_exec()` function [in the SPI framework] makes sure
that both `delay_usecs` & `delay` are used (in this order to preserve
backwards compatibility).

[1] commit bebcfd272d ("spi: introduce `delay` field for
`spi_transfer` + spi_transfer_delay_exec()")

Signed-off-by: Sergiu Cuciurean <sergiu.cuciurean@analog.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/adc/ad7292.c

@@ -122,7 +122,10 @@ static int ad7292_single_conversion(struct ad7292_state *st,
 		{
 			.tx_buf = &st->d8,
 			.len = 4,
-			.delay_usecs = 6,
+			.delay = {
+				.value = 6,
+				.unit = SPI_DELAY_UNIT_USECS
+			},
 		}, {
 			.rx_buf = &st->d16,
 			.len = 2,