media: venus: venc: Init the session only once in queue_setup

Init the hfi session only once in queue_setup and also cover that
with inst->lock.

Tested-by: Fritz Koenig <frkoenig@chromium.org>
Signed-off-by: Stanimir Varbanov <stanimir.varbanov@linaro.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>