staging: iio: resolver: ad2s1210: do not use fault register for dummy read

When reading registers on the AD2S1210 chip, we have to supply a "dummy"
address for the second SPI tx byte so that we don't accidentally write
to a register. This register will be read and the value discarded on the
next regmap read or write call.

Reading the fault register has a side-effect of clearing the faults
so we should not use this register for the dummy read.
Signed-off-by: David Lechner <dlechner@baylibre.com>
Link: https://lore.kernel.org/r/20231005-ad2s1210-mainline-v4-1-ec00746840fc@baylibre.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/staging/iio/resolver/ad2s1210.c

@@ -166,9 +166,10 @@ static int ad2s1210_regmap_reg_read(void *context, unsigned int reg,
 	st->tx[0] = reg;
 	/*
 	 * Must be valid register address here otherwise this could write data.
-	 * It doesn't matter which one.
+	 * It doesn't matter which one as long as reading doesn't have side-
+	 * effects.
 	 */
-	st->tx[1] = AD2S1210_REG_FAULT;
+	st->tx[1] = AD2S1210_REG_CONTROL;
 
 	ret = spi_sync_transfer(st->sdev, xfers, ARRAY_SIZE(xfers));
 	if (ret < 0)