media: venus: helpers: update NUM_MBS macro calculation

Consider alignment while calculating NUM_MBS.

Co-developed-by: Mansur Alisha Shaik <mansur@codeaurora.org>
Signed-off-by: Mansur Alisha Shaik <mansur@codeaurora.org>
Signed-off-by: Dikshita Agarwal <dikshita@codeaurora.org>
Signed-off-by: Stanimir Varbanov <stanimir.varbanov@linaro.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>