staging:iio:ad7606: Move set_drvdata() into common code
Both the platform_device and SPI driver call set_drvdata() at the end of
their probe function. Move this into the common probe() function to reduce
duplicated code.
Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>