radeon/uvd: fix a h265 context size bug

Signed-off-by: sonjiang <sonny.jiang@amd.com>
Cc: "12.0" <mesa-stable@lists.freedesktop.org>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
diff --git a/src/gallium/drivers/radeon/radeon_uvd.c b/src/gallium/drivers/radeon/radeon_uvd.c
index d4355fb..97765da 100644
--- a/src/gallium/drivers/radeon/radeon_uvd.c
+++ b/src/gallium/drivers/radeon/radeon_uvd.c
@@ -1096,6 +1096,9 @@
 			}
 			rvid_clear_buffer(decoder->context, &dec->ctx);
 		}
+
+		if (dec->ctx.res)
+			dec->msg->body.decode.dpb_reserved = dec->ctx.res->buf->size;
 		break;
 
 	case PIPE_VIDEO_FORMAT_VC1: