intel: Use rb->Data and rb->RowStride to handle spans Y flipping.

intel: Use rb->Data and rb->RowStride to handle spans Y flipping.

This is already pointing at 0 or Height - 1 and with an appropriate
pitch, so no need to recompute those values per customization of the
spans code.  Cuts 3 out of 21kb of the compiled size.

Reviewed-by: Chad Versace <chad@chad-versace.us>