nir: Validate that the sources of a phi have the same size as the destination
nir: Validate that the sources of a phi have the same size as the destination

Reviewed-by: Connor Abbott <71178acffcc112b21e5858656e5751f5e4aa9364@gmail.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler