drm/i915/gem/i915_gem_object: Demote non-kerneldoc header with no param descriptions

Fixes the following W=1 kernel build warning(s):

 drivers/gpu/drm/i915/gem/i915_gem_object.c:887: warning: Function parameter or member 'obj' not described in 'i915_gem_object_has_unknown_state'

Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Cc: David Airlie <airlied@gmail.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: "Christian König" <christian.koenig@amd.com>
Cc: Matthew Auld <matthew.auld@intel.com>
Cc: Nirmoy Das <nirmoy.das@intel.com>
Cc: intel-gfx@lists.freedesktop.org
Cc: dri-devel@lists.freedesktop.org
Cc: linux-media@vger.kernel.org
Cc: linaro-mm-sig@lists.linaro.org
Signed-off-by: Lee Jones <lee@kernel.org>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230331092607.700644-14-lee@kernel.org

drivers/gpu/drm/i915/gem/i915_gem_object.c

@@ -875,7 +875,7 @@ int i915_gem_object_wait_moving_fence(struct drm_i915_gem_object *obj,
 	return ret < 0 ? ret : 0;
 }
 
-/**
+/*
  * i915_gem_object_has_unknown_state - Return true if the object backing pages are
  * in an unknown_state. This means that userspace must NEVER be allowed to touch
  * the pages, with either the GPU or CPU.