drm/i915: Fix error path in i915_drm_resume_early

If system resume fails, this may lead to a runtime PM wake reference
underflow used for runtime PM state checking.

Fixes: 1f814dac

 ("drm/i915: add support for checking if we hold an RPM reference")
Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: http://patchwork.freedesktop.org/patch/msgid/1460963062-13211-2-git-send-email-imre.deak@intel.com