i965/fs: Fix unused variable warning
i965/fs: Fix unused variable warning

Annotate offset_components with attribute 'unused'.

Reviewed-by: Matt Turner <789b315743a28dd066a4ba1459c35951c291d8a6@gmail.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler