drm/amd/display: Fix arithmetic error in MALL size calculations for subvp

[Description]
Need to subtract unused section of the viewport when calculating required space
in MALL for subvp instead of adding, to prevent over allocation.
Reviewed-by: Alvin Lee <Alvin.Lee2@amd.com>
Acked-by: Jasdeep Dhillon <jdhillon@amd.com>
Signed-off-by: Dillon Varone <Dillon.Varone@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/dcn32/dcn32_resource_helpers.c

@@ -97,14 +97,14 @@ uint32_t dcn32_helper_calculate_num_ways_for_subvp(struct dc *dc, struct dc_stat
 			 * FLOOR(vp_x_start, blk_width)
 			 */
 			full_vp_width_blk_aligned = ((pipe->plane_res.scl_data.viewport.x +
-					pipe->plane_res.scl_data.viewport.width + mblk_width - 1) / mblk_width * mblk_width) +
+					pipe->plane_res.scl_data.viewport.width + mblk_width - 1) / mblk_width * mblk_width) -
 					(pipe->plane_res.scl_data.viewport.x / mblk_width * mblk_width);
 
 			/* full_vp_height_blk_aligned = FLOOR(vp_y_start + full_vp_height + blk_height - 1, blk_height) -
 			 * FLOOR(vp_y_start, blk_height)
 			 */
 			full_vp_height_blk_aligned = ((pipe->plane_res.scl_data.viewport.y +
-					full_vp_height + mblk_height - 1) / mblk_height * mblk_height) +
+					full_vp_height + mblk_height - 1) / mblk_height * mblk_height) -
 					(pipe->plane_res.scl_data.viewport.y / mblk_height * mblk_height);
 
 			/* mall_alloc_width_blk_aligned_l/c = full_vp_width_blk_aligned_l/c */