Drivers/DisplayLink/DisplayLinkPkg DisplayLinkGop

Corrected initialisation of one of data structures used to transmit USB
control messages. Mistake had no practical effects but fixing to be on safe
side.

Cc: Leif Lindholm <leif.lindholm@linaro.org>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Andy Hayes <andy.hayes@displaylink.com>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>