drm/dp: fix a kernel-doc issue at drm_edid.c

The name of the argument is different, causing those warnings:

	./drivers/gpu/drm/drm_edid.c:3754: warning: Function parameter or member 'video_code' not described in 'drm_display_mode_from_cea_vic'
	./drivers/gpu/drm/drm_edid.c:3754: warning: Excess function parameter 'vic' description in 'drm_display_mode_from_cea_vic'

Fixes: 7af655bc ("drm/dp: Add drm_dp_downstream_mode()")
Reviewed-by: Lyude Paul <lyude@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/7f4d6c3ff6df63ebd006eb90a5108006c23e2168.1603791716.git.mchehab+huawei@kernel.org