drm/i915: Fix logical inversion for gen4 quirking

The assertion that we want to make before disabling the pin of the pages
for the unknown swizzling quirk is that the quirk is indeed active, and
that the quirk is disabled before we do apply it to the pages.

Fixes: 2c3a3f44 ("drm/i915: Fix pages pin counting around swizzle quirk")
Fixes: 957870f9 ("drm/i915: Split out i915_gem_object_set_tiling()")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170521124014.27678-1-chris@chris-wilson.co.uk
Reviewed-bhy: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>