i965/fs: Only do CSE when the dst types match.

i965/fs: Only do CSE when the dst types match.

We could potentially do some CSE even when the dst types aren't the same
on gen6 where there is no implicit dst type conversion iirc, or in the
case of uniform pull constant loads where the dst type doesn't impact
what's stored.  But it's not worth worrying about.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
NOTE: This is a candidate for the 9.1 branch.