media: rkvdec:Remove redundant memset

As dma_alloc_coherent() will return a zeroed buffer, we
don't need to memset the returned buffer.
priv_tbl = dma_alloc_coherent() and count_tbl = dma_alloc_coherent()
should be enough.

-see commit 750afb08

 ("cross-tree: phase out dma_zalloc_coherent()")

Signed-off-by: Zhang Zekun <zhangzekun11@huawei.com>
Reviewed-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>