drm/msm/dpu: use drm_rect_fp_to_int()

Use the drm_rect_fp_to_int() helper instead of using the hand-written
code.

Reviewed-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/621476/
Link: https://lore.kernel.org/r/20241025-dpu-virtual-wide-v6-1-0310fd519765@linaro.org

Author: lumag

drivers/gpu/drm/msm/disp/dpu1/dpu_plane.c

@@ -829,13 +829,8 @@ static int dpu_plane_atomic_check(struct drm_plane *plane,
 		return -EINVAL;
 	}
 
-	pipe_cfg->src_rect = new_plane_state->src;
-
 	/* state->src is 16.16, src_rect is not */
-	pipe_cfg->src_rect.x1 >>= 16;
-	pipe_cfg->src_rect.x2 >>= 16;
-	pipe_cfg->src_rect.y1 >>= 16;
-	pipe_cfg->src_rect.y2 >>= 16;
+	drm_rect_fp_to_int(&pipe_cfg->src_rect, &new_plane_state->src);
 
 	pipe_cfg->dst_rect = new_plane_state->dst;