Documentation: connector: Update the description of sink-vdos

Remove the acronym "VDM" and replace it with the full name "Vendor
Defined Message".

Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Kyle Tso <kyletso@google.com>
Link: https://lore.kernel.org/r/20210212073743.665038-1-kyletso@google.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>