media: ad5820: Add support for of-autoload

Since kernel 4.16, i2c devices with DT compatible tag are modprobed
using their DT modalias.
Without this patch, if this driver is build as module it would never
be autoprobed.

There is no need to mask it with CONFIG_OF to allow ACPI loading, this
also builds find with CONFIG_OF=n.

Signed-off-by: Ricardo Ribalda Delgado <ribalda@kernel.org>
Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>