iio: dac: ad5593r: Fix i2c read protocol requirements

[mhennerich]

For reliable operation across the full range of supported interface rates. The AD5593R needs a STOP condition between address write, and data read (like show in the datasheet Figure 40) so in turn i2c_smbus_read_word_swapped cannot be used.

See here: https://ez.analog.com/linux-software-drivers/f/q-a/560845/ad5593r-missing-i2c-stop-bit-in-linux-driver/466631