drm/i915/dsc: Fix pic_width readout

pic_width when written into the PPS register is divided by the no.
of vdsc instances first but the actual variable that we compare it
to does not change i.e vdsc_cfg->pic_width hence when reading the
register back for pic_width it needs to be multiplied by
num_vdsc_instances rather than being divided.

Fixes: 8b70b569 ("drm/i915/vdsc: Fill the intel_dsc_get_pps_config function")
Signed-off-by: Suraj Kandpal <suraj.kandpal@intel.com>
Reviewed-by: Chaitanya Kumar Borah <chaitanya.kumar.borah@intel.com>
Signed-off-by: Animesh Manna <animesh.manna@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230911193742.836063-1-suraj.kandpal@intel.com