drm/i915: Provide argument names for static stubs

Make sure we keep kbuilder happy in all of its random configs by
providing argument names for compile-time stubs.

In file included from drivers/gpu/drm/i915/intel_dp_mst.c:27:0:
   drivers/gpu/drm/i915/i915_drv.h: In function 'i915_debugfs_register':
>> drivers/gpu/drm/i915/i915_drv.h:3612:48: error: parameter name omitted
    static inline int i915_debugfs_register(struct drm_i915_private *) {return 0;}
                                                   ^~~~~~~~~~~~~~~~
   drivers/gpu/drm/i915/i915_drv.h: In function 'i915_debugfs_unregister':
   drivers/gpu/drm/i915/i915_drv.h:3613:51: error: parameter name omitted
    static inline void i915_debugfs_unregister(struct drm_i915_private *) {}

Reported-by: 0day
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1468324529-20461-1-git-send-email-chris@chris-wilson.co.uk