media: renesas: vsp1: Simplify partition calculation

When calculation a partition in vsp1_pipeline_calculate_partition(),
there is no need to handle the case where the whole image is covered by
a single partition locally. In that case, the index and div_size
parameters are 0 and format->width respectively, which makes the general
code behave exactly as the special case. Drop the special case.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Reviewed-by: Jacopo Mondi <jacopo.mondi+renesas@ideasonboard.com>