i965/fs: Properly handle LOAD_PAYLOAD in fs_inst::regs_read
i965/fs: Properly handle LOAD_PAYLOAD in fs_inst::regs_read

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

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler