media: venus: venc: Make the range of us_per_frame explicit

Fps bigger than 0.000232829 fps, this fits in a 32 bit us_per_frame.
There is no need to do a 64 bit division here.

Also, the driver only works with whole fps.

Found with cocci:
drivers/media/platform/qcom/venus/venc.c:418:1-7: WARNING: do_div() does a 64-by-32 division, please consider using div64_u64 instead.

Reviewed-by: Vikash Garodia <quic_vgarodia@quicinc.com>
Reviewed-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
Signed-off-by: Bryan O'Donoghue <bod@kernel.org>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>