dt-bindings: vendor-prefixes: add osmc prefix

Open Source Media Centre (Sam Nazarko Trading Ltd.) are a manufacturer
of Linux Set-Top Box devices.

Signed-off-by: Christian Hewitt <christianshewitt@gmail.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Link: https://lore.kernel.org/r/20220211105311.30320-2-christianshewitt@gmail.com