st/mesa: only flip stipple pattern for winsys fbo's

st/mesa: only flip stipple pattern for winsys fbo's

Gallium is completely oblivious to whether the fbo is flipped or not.
Only flip the stipple pattern when the fbo is flipped as well. Otherwise
the driver has no idea when to unflip the pattern.

Fixes bin/gl-2.1-polygon-stipple-fs -fbo

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Reviewed-by: Brian Paul <brianp@vmware.com>
Tested-by: Brian Paul <brianp@vmware.com>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>