media: mtk-vcodec: fix access to vb2_v4l2_buffer struct

Commit 0650a91499e0 ("media: mtk-vcodec: Correct return type for mem2mem
buffer helpers") fixed the return types for mem2mem buffer helper
functions, but omitted two occurrences that are accessed in the
mtk_v4l2_debug() macro. These only trigger compiler errors when DEBUG is
defined.

Fixes: 0650a91499e0 ("media: mtk-vcodec: Correct return type for mem2mem buffer helpers")

Signed-off-by: Alexandre Courbot <[e-mail]>
Signed-off-by: Hans Verkuil <[e-mail]>
Signed-off-by: Mauro Carvalho Chehab <[e-mail]>

drivers/media/platform/mtk-vcodec/mtk_vcodec_dec.c

···
 	src_mem.size = (size_t)src_buf->planes[0].bytesused;
 	mtk_v4l2_debug(2,
 			"[%d] buf id=%d va=%p dma=%pad size=%zx",
-			ctx->id, src_buf->index,
+			ctx->id, src_buf->vb2_buf.index,
 			src_mem.va, &src_mem.dma_addr,
 			src_mem.size);
 
···
 		}
 		mtk_v4l2_debug(ret ? 0 : 1,
 			       "[%d] vdec_if_decode() src_buf=%d, size=%zu, fail=%d, res_chg=%d",
-			       ctx->id, src_buf->index,
+			       ctx->id, src_buf->vb2_buf.index,
 			       src_mem.size, ret, res_chg);
 		return;
 	}