drm/msm: Add missing num_dspp field documentation

Somehow documentation for num_dspp was missed, so add that
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Signed-off-by: Vinod Koul <vkoul@kernel.org>
Patchwork: https://patchwork.freedesktop.org/patch/480924/
Link: https://lore.kernel.org/r/20220406094031.1027376-10-vkoul@kernel.orgSigned-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>

drivers/gpu/drm/msm/msm_drv.h

@@ -92,6 +92,7 @@ enum msm_event_wait {
  * @num_lm:       number of layer mixers used
  * @num_enc:      number of compression encoder blocks used
  * @num_intf:     number of interfaces the panel is mounted on
+ * @num_dspp:     number of dspp blocks used
  */
 struct msm_display_topology {
 	u32 num_lm;