ARM: dts: bcm283x: Disable dsi0 node

Since its inception the module was meant to be disabled by default, but
the original commit failed to add the relevant property.

Fixes: 4aba4cf8 ("ARM: dts: bcm2835: Add the DSI module nodes and clocks")
Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Reviewed-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>