iris: Avoid double flushing in iris_transfer_flush_region when copying.

iris: Avoid double flushing in iris_transfer_flush_region when copying.

My intention was to have iris_copy_region not do flushing, and leave
that up to the callers.  iris_resource_copy_region needs to do this,
but iris_transfer_flush_region was already doing it.  The net result
was that we were doing it twice for transfers.

So, move the flushing from iris_copy_region to iris_resource_copy_region
so that it only happens in the callers as I intended.