dt-bindings: display: look for dsi* nodes in dsi-controller

Rob wrote:

    Uhhh, it's looking for dsi-controller(@.*)? which is not the common
    case found in dts files. We should fix that to dsi(@.*)?.

See: https://lore.kernel.org/dri-devel/20200319032222.GK29911@bogus/



Fix it.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: Rob Herring <robh@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200408195109.32692-3-sam@ravnborg.org