svga: fix test for SVGA_NEW_STIPPLE

svga: fix test for SVGA_NEW_STIPPLE

We only want to set the SVGA_NEW_STIPPLE dirty flag when the polygon
stipple state changes.  Before, we only set the flag when we were
enabling stipple, but not disabling.

We don't really have to add SVGA_NEW_STIPPLE to the dirty FS state
set since it's a subset of SVGA_NEW_RAST, but let's be explicit.

This doesn't fix any known bugs.

Reviewed-by: Charmaine Lee <charmainel@vmware.com>