drm/vc4: Correct arithmetic for shifting between columns of SAND images

Commit 69dbba7 ("drm/vc4: Add algorithmic handling for SAND")
lost a multiplication by the tile width when doing the pointer arithmetic
for cropping off columns for vc6.

Correct that computation.

Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.com>

Author: 6by9

drivers/gpu/drm/vc4/vc4_plane.c

@@ -1992,7 +1992,7 @@ static int vc6_plane_mode_set(struct drm_plane *plane,
 
 			tile = src_x / pix_per_tile;
 
-			offsets[i] += pitch[i] * tile;
+			offsets[i] += pitch[i] * tile * tile_width;
 			offsets[i] += src_y / (i ? v_subsample : 1) * tile_width;
 			offsets[i] += x_off & ~(i ? 1 : 0);