anv/device: Actually free the CPU-side fence struct again
anv/device: Actually free the CPU-side fence struct again

In 23de78768, when we switched from allocating individual BOs to using the
pool for fences, we accidentally deleted the free.

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler