media: venus: Use newly-introduced hfi_buffer_requirements accessors

Now that we have a way which is independent of the HFI version to set
the correct fields in hfi_buffer_requirements, use it!

Signed-off-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Signed-off-by: Stanimir Varbanov <stanimir.k.varbanov@gmail.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>