i965: Combine src/dest tex vs. rb checks in intel_copy_image_sub_data.

i965: Combine src/dest tex vs. rb checks in intel_copy_image_sub_data.

This simplifies things a little - now we only have one (tex or rb?)
if-ladder for src, and a second for dst, rather than four.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Anuj Phogat <anuj.phogat@gmail.com>
Reviewed-by: Chris Forbes <chrisforbes@google.com>