drm/msm/dpu: correct struct dpu_encoder_virt docs

Fix a typo in struct dpu_encoder_virt kerneldoc, which made it ignore
description of the cwb_mask field.

Fixes: dd331404 ("drm/msm/dpu: Configure CWB in writeback encoder")
Signed-off-by: Dmitry Baryshkov <lumag@kernel.org>
Reviewed-by: Rob Clark <robdclark@gmail.com>
Patchwork: https://patchwork.freedesktop.org/patch/641315/
Link: https://lore.kernel.org/r/20250306-dpu-fix-docs-v1-2-e51b71e8ad84@kernel.org


Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>