iio: dac: ad5686: fix input raw value check

iio: dac: ad5686: fix input raw value check

Fix range check for input raw value, which is off by one, i.e., for a
10-bit DAC the max valid value is 1023, but 1 << 10 equals 1024, which
passes the previous check, allowing an out-of-range write. The issue
exists since the ad5686 driver was first introduced.

Fixes: c2f37c8dcadc ("iio: dac: New driver for AD5686R, AD5685R, AD5684R Digital to analog converters")
Reviewed-by: Andy Shevchenko <andriy.shevchenko@intel.com>
Signed-off-by: Rodrigo Alencar <rodrigo.alencar@analog.com>
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>