arm64: dts: r8a7795: salvator-xs: Connect DU dot clocks 0 and 3

The DU dot clocks 0 and 3 are provided by the programmable VC6 clock
generator. Connect them to the clock source node.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>