drm/i915: Rebalance runtime pm vs forcewake

Calling intel_runtime_pm_put() is illegal from a soft-irq context, so
revert the crude hack

commit aa0b3b5b
Author: Paulo Zanoni <paulo.r.zanoni@intel.com>
Date:   Tue Apr 1 14:55:07 2014 -0300

    drm/i915: don't schedule force_wake_timer at gen6_read

and apply the single line corrective instead.

v2: assert forcewake is off after the forcewake_reset (Paulo)

References: https://bugs.freedesktop.org/show_bug.cgi?id=80913


Cc: Paulo Zanoni <paulo.r.zanoni@intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Mika Kuoppala <mika.kuoppala@intel.com>
Reviewed-by: Deepak S <deepak.s@linux.intel.com> (v1)
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>