drm/i915: don't get/put runtime PM at the debugfs forcewake file

Because gen6_gt_force_wake_{get,put} should already be responsible for
getting/putting runtime PM. If we keep these calls, debugfs will not
be testing the get/put calls of the forcewake functions.

Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>