media: venus: vdec: fix decoded data size

[ Upstream commit ce32c0a530bd955206fe45c2eff77e581202d699 ]

Existing code returns the max of the decoded size and buffer size.
It turns out that buffer size is always greater due to hardware
alignment requirement. As a result, payload size given to client
is incorrect. This change ensures that the bytesused is assigned
to actual payload size, when available.

Signed-off-by: Vikash Garodia <vgarodia@codeaurora.org>
Acked-by: Stanimir Varbanov <stanimir.varbanov@linaro.org>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>