drm/i915: Squelch WARN for VLV_COUNTER_CONTROL

Before rc6 is initialised (after driver load or resume), the value inside
VLV_COUNTER_CONTROL is undefined so we cannot make an assertion that is
in HIGH_RANGE mode.

Fixes: 6b7f6aa7 ("drm/i915: Use coarse grained residency counter with byt")
Testcase: igt/drv_suspend/debugfs-reader
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Mika Kuoppala <mika.kuoppala@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170317125918.11351-1-chris@chris-wilson.co.uk


Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com>