media: mtk-vcodec: fix error return code in vdec_vp9_decode()

Fix to return a negative error code from the error handling
case instead of 0, as done elsewhere in this function.

Fixes: dea42fb7 ("media: mtk-vcodec: reset segment data then trig decoder")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Zhang Changzhong <zhangchangzhong@huawei.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>