i965/fs: Make scratch write instructions use the correct execution size
i965/fs: Make scratch write instructions use the correct execution size

Reviewed-by: Kristian Høgsberg <ca9b5b1e27d4fa7f4ba6848bdd08ca52cfd6330c@bitplanet.net>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler