i965/fs: Fix code emission for imul_high in NIR.
i965/fs: Fix code emission for imul_high in NIR.

Copy over from brw_fs_visitor.cpp.

Reviewed-by: Kenneth Graunke <bd2562f754ec92342f93f61c25d731e290a2ffa8@whitecape.org>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler