iio: adc: xilinx: Fix register addresses

Define the register addresses for MIN_VCCPINT, MIN_VCCPAUX, MIN_VCCO_DDR
correctly.

Signed-off-by: Thomas Betker <thomas.betker@rohde-schwarz.com>
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>