media: venus: venus_helper_get_bufreq(): req is never NULL

Fix a smatch error:

drivers/media/platform/qcom/venus/helpers.c: drivers/media/platform/qcom/venus/helpers.c:678 venus_helper_get_bufreq() error: we previously assumed 'req' could be null (see line 674)

After checking how venus_helper_get_bufreq() is called it is clear that
req is never NULL, so just drop the checks.

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Stanimir Varbanov <stanimir.varbanov@linaro.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>