i965/fs: Estimate number of registers written correctly in opt_register_renaming.
i965/fs: Estimate number of registers written correctly in opt_register_renaming.

The current estimate is incorrect for non-32b types.

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

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler