drivers/iio/adc/cf_axi_jesd204b: Add reg_access

Signed-off-by: Michael Hennerich <michael.hennerich@analog.com>
drivers/iio/adc/cf_axi_jesd204b: Temporary workaround reset JESD IP twice

Signed-off-by: Michael Hennerich <michael.hennerich@analog.com>