pipe-loader: meson: reference correct library

The library is called libgalliumvl_stub - note singular.

Fixes: 42ea0631 ("meson: build clover")
Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Dylan Baker <dylan@pnwbakers.com>
(cherry picked from commit 2eedb79e)