drm/i915: Rename __force_wake_get to __force_wake_auto

__force_wake_get() only acquires a temporary wakeref on forcewake that is
automatically released when a timer expires. When reading the code
again, I confused __intel_uncore_forcewake_get() for __force_wake_get()
and to my shame thought I found a bug in unbalanced wake_count handling.

I claim that if the function had been called __force_wake_auto() instead
I would not have embarrassed myself.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1458829907-26596-1-git-send-email-chris@chris-wilson.co.uk
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>