nir/spirv: zero out value array
nir/spirv: zero out value array

Before values are pushed or annotated with a name, decoration, etc.,
they need to have an invalid type, NULL name, NULL decoration, etc.
ralloc zero's everything by accident, so this wasn't an issue in
practice, but we should be explicitly zero'ing it.

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler