media: platform: mtk-mdp3: fix error handling in mdp_cmdq_send()

Increase and refine the goto label in mdp_cmdq_send() to avoid
double free and facilitate traceability.
Also, remove redundant work queue event in blocking function
mdp_cmdq_send().

Fixes: 61890cca ("media: platform: mtk-mdp3: add MediaTek MDP3 driver")
Signed-off-by: Moudy Ho <moudy.ho@mediatek.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>