media: dt-bindings: adv748x: Fix decimal unit addresses

With recent dtc and W=1:

    Warning (graph_port): video-receiver@70/port@10: graph node unit address error, expected "a"
    Warning (graph_port): video-receiver@70/port@11: graph node unit address error, expected "b"

Unit addresses are always hexadecimal (without prefix), while the bases
of reg property values depend on their prefixes.

Fixes: e6959517 ("media: adv748x: Add adv7481, adv7482 bindings")

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>