ad5758_spi_reg_read
regval = ad5758_spi_reg_read(st, addr);
ret = ad5758_spi_reg_read(st, reg);
ret = ad5758_spi_reg_read(st, reg);
ret = ad5758_spi_reg_read(st, AD5758_DAC_INPUT);
regval = ad5758_spi_reg_read(st, AD5758_DIGITAL_DIAG_RESULTS);