ASoC: dapm-graph: set fill colour of turned on nodes

Some tools like KGraphViewer interpret the "ON" nodes not having an
explicitly set fill colour as them being entirely black, which obscures
the text on them and looks funny. In fact, I thought they were off for
the longest time. Comparing to the output of the `dot` tool, I assume
they are supposed to be white.

Instead of speclawyering over who's in the wrong and must immediately
atone for their wickedness at the altar of RFC2119, just be explicit
about it, set the fillcolor to white, and nobody gets confused.

Signed-off-by: Nicolas Frattaroli <nicolas.frattaroli@collabora.com>
Tested-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
Reviewed-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
Link: https://patch.msgid.link/20250221-dapm-graph-node-colour-v1-1-514ed0aa7069@collabora.com


Signed-off-by: Mark Brown <broonie@kernel.org>