drm/i915: fix order of fence release wrt flushing

i915_gem_object_unbind had the ordering wrong. The other user,
i915_gem_object_put_fence_reg already has the correct ordering.

Results was usually corrupted pixmaps, especially garbled font glyphs
after a suspend/resume (because this evicts everything).

I'm still waiting for the feedback from the bug-reporters, but
because this obviously fixes a bug (at least for me) I'm already
submitting it.

Bugzilla: http://bugs.freedesktop.org/show_bug.cgi?id=25406


Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Eric Anholt <eric@anholt.net>
CC: stable@kernel.org