drm/i915: fix intel_frontbuffer_flip documentation

Reported by the kbuild test robot.

Regression introduced by:
commit fdbff928
Author: Daniel Vetter <daniel.vetter@ffwll.ch>
Date:   Thu Jun 18 11:23:24 2015 +0200
    drm/i915: Clear fb_tracking.busy_bits also for synchronous flips

(I reviewed this commit, so it's also my fault)
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

Documentation/DocBook/drm.tmpl

@@ -4012,7 +4012,6 @@ int num_ioctls;</synopsis>
         <title>Frontbuffer Tracking</title>
 !Pdrivers/gpu/drm/i915/intel_frontbuffer.c frontbuffer tracking
 !Idrivers/gpu/drm/i915/intel_frontbuffer.c
-!Fdrivers/gpu/drm/i915/intel_drv.h intel_frontbuffer_flip
 !Fdrivers/gpu/drm/i915/i915_gem.c i915_gem_track_fb
       </sect2>
       <sect2>

drivers/gpu/drm/i915/intel_frontbuffer.c

@@ -229,7 +229,6 @@ void intel_frontbuffer_flip_complete(struct drm_device *dev,
  *
  * Can be called without any locks held.
  */
-
 void intel_frontbuffer_flip(struct drm_device *dev,
 			    unsigned frontbuffer_bits)
 {