media: platform: mtk-mdp3: fix error code in mdp_vpu_dev_init()

Return a negative error code if mdp_vpu_shared_mem_alloc() fails.

Fixes: 61890cca ("media: platform: mtk-mdp3: add MediaTek MDP3 driver")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: Matthias Brugger <matthias.bgg@gmail.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>