staging: iio: resolver: ads1210: fix config mode

staging: iio: resolver: ads1210: fix config mode

As stated in the device datasheet [1], bits a0 and a1 have to be set to
1 for the configuration mode.

[1]: https://www.analog.com/media/en/technical-documentation/data-sheets/ad2s1210.pdf

Fixes: b19e9ad5e2cb9 ("staging:iio:resolver:ad2s1210 general driver cleanup")
Cc: stable <stable@kernel.org>
Signed-off-by: Nuno Sá <nuno.sa@analog.com>
Link: https://lore.kernel.org/r/20230327145414.1505537-1-nuno.sa@analog.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>