iio:dac:ad5686: Move exports into IIO_AD5686 namespace

Note these are used in the related ad5696-i2c drivers as well as the
more obviously connected ad5686-spi driver.

In order to avoid unnecessary pollution of the global symbol namespace
move the common/library functions into a specific namespace and import
that into the various specific device drivers that use them.

For more information see https://lwn.net/Articles/760045/

Signed-off-by: Jonathan Cameron <[e-mail]>
Reviewed-by: Andy Shevchenko <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

drivers/iio/dac/ad5686-spi.c

···
 MODULE_AUTHOR("Stefan Popa <[e-mail]>");
 MODULE_DESCRIPTION("Analog Devices AD5686 and similar multi-channel DACs");
 MODULE_LICENSE("GPL v2");
+MODULE_IMPORT_NS(IIO_AD5686);

drivers/iio/dac/ad5686.c

···
 		regulator_disable(st->reg);
 	return ret;
 }
-EXPORT_SYMBOL_GPL(ad5686_probe);
+EXPORT_SYMBOL_NS_GPL(ad5686_probe, IIO_AD5686);
 
 void ad5686_remove(struct device *dev)
 {
···
 	if (!IS_ERR(st->reg))
 		regulator_disable(st->reg);
 }
-EXPORT_SYMBOL_GPL(ad5686_remove);
+EXPORT_SYMBOL_NS_GPL(ad5686_remove, IIO_AD5686);
 
 MODULE_AUTHOR("Michael Hennerich <[e-mail]>");
 MODULE_DESCRIPTION("Analog Devices AD5686/85/84 DAC");

drivers/iio/dac/ad5696-i2c.c

···
 MODULE_AUTHOR("Stefan Popa <[e-mail]>");
 MODULE_DESCRIPTION("Analog Devices AD5686 and similar multi-channel DACs");
 MODULE_LICENSE("GPL v2");
+MODULE_IMPORT_NS(IIO_AD5686);