Documentation: gpu/drm-uapi: eliminate duplicated word

Drop the doubled word "when".

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: linux-doc@vger.kernel.org
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: dri-devel@lists.freedesktop.org
Link: https://lore.kernel.org/r/20200707180414.10467-8-rdunlap@infradead.org


Signed-off-by: Jonathan Corbet <corbet@lwn.net>