drm/rockchip: inno-hdmi: switch to FIELD_PREP_WM16 macro

The era of hand-rolled HIWORD_UPDATE macros is over, at least for those
drivers that use constant masks.

The inno-hdmi driver's own HIWORD_UPDATE macro is instantiated only
twice. Remove it, and replace its uses with FIELD_PREP_WM16. Since
FIELD_PREP_WM16 shifts the value for us, we replace using the mask as
the value by simply using 1 instead.

With the new FIELD_PREP_WM16 macro, we gain better error checking and a
central shared definition.

This has been compile-tested only as I lack hardware this old, but the
change is trivial enough that I am fairly certain it's equivalent.

Signed-off-by: Nicolas Frattaroli <nicolas.frattaroli@collabora.com>
Reviewed-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Yury Norov (NVIDIA) <yury.norov@gmail.com>