drm/amd/display: Fix recout calculation for stereo side-by-side

[why & how]
The recout x offset was incorrect which led to
wrong viewport calculation. For stereo
side-by-side case, the slice index should be
0 for both split pipes.
Reviewed-by: Dmytro Laktyushkin <dmytro.laktyushkin@amd.com>
Acked-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Signed-off-by: Sung Joon Kim <sungjoon.kim@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/core/dc_resource.c

@@ -950,6 +950,9 @@ static struct rect calculate_mpc_slice_in_timing_active(
 			stream->view_format != VIEW_3D_FORMAT_SIDE_BY_SIDE ||
 			mpc_rec.width % 2 == 0);
 
+	if (stream->view_format == VIEW_3D_FORMAT_SIDE_BY_SIDE)
+		mpc_rec.x -= (mpc_rec.width * mpc_slice_idx);
+
 	/* extra pixels in the division remainder need to go to pipes after
 	 * the extra pixel index minus one(epimo) defined here as:
 	 */