etnaviv: stop leaking the dummy texure descriptor BO

Free the dummy texture descriptor BO on context destroy.

Fixes: eda73d7127 (etnaviv: GC7000: Texture descriptors)
Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Reviewed-by: Guido Günther <agx@sigxcpu.org>
Reviewed-by: Christian Gmeiner <christian.gmeiner@gmail.com>
Cc: <mesa-stable@lists.freedesktop.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6986>

src/gallium/drivers/etnaviv/etnaviv_context.c

@@ -130,6 +130,9 @@ etna_context_destroy(struct pipe_context *pctx)
    }
    mtx_unlock(&ctx->lock);
 
+   if (ctx->dummy_desc_bo)
+      etna_bo_del(ctx->dummy_desc_bo);
+
    if (ctx->dummy_rt)
       etna_bo_del(ctx->dummy_rt);