drm/amdgpu/mn: fix documentation for amdgpu_mn_read_lock

Document the new parameter.

Fixes: 93065ac7 ("mm, oom: distinguish blockable mode for mmu notifiers")
Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/amdgpu_mn.c

@@ -136,6 +136,7 @@ void amdgpu_mn_unlock(struct amdgpu_mn *mn)
  * amdgpu_mn_read_lock - take the read side lock for this notifier
  *
  * @amn: our notifier
+ * @blockable: is the notifier blockable
  */
 static int amdgpu_mn_read_lock(struct amdgpu_mn *amn, bool blockable)
 {