mesa: only copy the requested teximage faces

mesa: only copy the requested teximage faces

Cube maps are special in that they have separate teximages for each
face. We handled that by copying the data to them separately, but in
case zoffset != 0 or depth != 6 we would read off the end of the client
array or modify the wrong images.

zoffset/depth have already been verified by the time the code gets to
this stage, so no need to double-check.

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Reviewed-by: Brian Paul <brianp@vmware.com>
Cc: "10.6 11.0" <mesa-stable@lists.freedesktop.org>