venus: fix a prime blit assert

The assert doesn't consider multiple queue family case where the same
blit cmd has to be recorded for each, thus hitting the assert for the
same image and buffer.

Fixes: 5535184539 ("venus: track prime blit dst buffer memory in the wsi image")
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/35984>

src/virtio/vulkan/vn_command_buffer.c

@@ -1490,7 +1490,7 @@ vn_CmdCopyImageToBuffer(VkCommandBuffer commandBuffer,
    if (buf->wsi.mem) {
       assert(img->wsi.is_wsi);
       assert(img->wsi.is_prime_blit_src);
-      assert(!img->wsi.blit_mem);
+      assert(!img->wsi.blit_mem || img->wsi.blit_mem == buf->wsi.mem);
       img->wsi.blit_mem = buf->wsi.mem;
    }