i965/fs: Return progress from move_interpolation_to_top().
i965/fs: Return progress from move_interpolation_to_top().

And mark as static at the same time.

Reviewed-by: Jason Ekstrand <68c46a606457643eab92053c1c05574abb26f861@jlekstrand.net>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler