media: venus: venc: amend buffer size for bitstream plane

Accept the buffer size requested by client and compare it
against driver calculated size and set the maximum to
bitstream plane.

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