drm/i915: fixup interrupted overlay switch off calls

When switching to interruptible sleeps in the overlay code, I've
forgotten to recover from interruptions at one site.  This
resulted in the overlay still running when it should have been
switched off. This in turn caused a hang on resume because it
tried to disable the (not-running) overlay in preparation for the
resume modeset.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=24980


Tested-by:  <maximlevitsky@gmail.com>

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