media: venus: helpers: fix dynamic buffer mode for v4

Venus v4 doesn't send ALLOC_MODE property and thus parser doesn't
recognize it as dynamic buffer (for OUTPUT/OUTPUT2 type of buffers)
make it obvious in the helper function.

Signed-off-by: Stanimir Varbanov <stanimir.varbanov@linaro.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>