media: phy-rockchip-dphy-rx0: Drop unneeded CONFIG_OF dependency

The driver is perfectly capable of being built without CONFIG_OF.
Remove this dependency, which is useful for compile-only tests.

Signed-off-by: Ezequiel Garcia <ezequiel@collabora.com>
Acked-by: Helen Koike <helen.koike@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>